A national tilt rightward four years ago carried Ronald Reagan into the White House and the Republican Party to its surprise takeover of the United States Senate.
But the fight in 1984 for control of the upper chamber of Congress is shaping up as a series of battles in the political hills and valleys of 33 states.
Republicans have most of the liabilities. They are losing majority leader Howard H. Baker Jr. of Tennessee, who is retiring. Nineteen of the GOP's 55 seats are up for grabs, and several of these are listed by both sides as vulnerable. The Democrats must defend only 14 seats, and their prospects look bright in almost every case.
Even if President Reagan, with his current popularity, wins handily, he may offer little aid in Senate races. Democrats are quick to point to Republican Richard Nixon, who won a reelection landslide in 1972, while his party lost two Senate seats.
''People are afraid of what an unconstrained Ronald Reagan will do'' in foreign affairs, argues J. Brian Atwood, director of the Democratic Senatorial Campaign Committee. He says the public will want Democrats on Capitol Hill as a balance.
Sen. Richard G. Lugar, chairman of the National Republican Senatorial Committee, holds limited hopes for Reagan coattails. ''I think Reagan will win big,'' the Indiana senator says and adds that he expects an election-day surge that will help Republicans in close races.
The GOP has trumpeted the call to arms - or at least to donations - for the challenge to their newfound control of the Senate, and the dollars have poured in. The Republican senatorial committee plans to have $25 million to spend, while the Democratic senatorial committee will have only about $5 million.
But the keynote for Republican Senate races this year is neither the President nor campaign money. It is the economy. After a deep recession, with its month-by-month drumbeat of worsening unemployment, the current economic news is music to GOP ears.
Republican senators with only so-so approval ratings now have an economy to hitch their campaign wagons to.
''The recovery is firmly under way,'' an upbeat Sen. Roger W. Jepsen told a recent Kiwanis Club meeting in Des Moines. The first-term Iowa Republican has had low approval ratings and criticism for his undistinguished performance in Washington. He is considered beatable.
His message to Iowa is simple: Now that the economic picture is improving, the worst thing voters can do is change directions in midstream. Which, of course, means that the best thing to do is keep Republicans like Mr. Jepsen in office.
Even in hard-pressed Illinois, Republican incumbent Sen. Charles H. Percy points to improved conditions. The state has faced double-barreled woes, with the decline of its heavy industry and a crop-devastating drought. But unemployment, still higher than national levels, has now dipped below 10 percent in Illinois.
Times are still rough in pockets across the state. In tiny downstate Windsor, the walls of the Country Kitchen dinette recently displayed two posters advertising sales of farm machinery, the latest in a long chain of bankruptcy auctions. Local factories are operating on reduced shifts, and some have shut down permanently.
But hopes for recovery are reaching some areas of Illinois. ''Are you better off than three years ago?'' said Senator Percy, echoing a Reagan campaign theme recently as he spoke to home builders meeting in the prosperous Chicago suburb of Naperville. He then listed the administration's successes in reducing inflation, trimming the rate of government growth, and cutting taxes.
Automakers are on overtime, home starts are up, and retail sales were ''never better'' last Christmas, Percy told the mostly Republican group. ''In other words, we've fulfilled our pledges,'' he said.
''The economic issue is still the issue for two-thirds of all Americans,'' the GOP's Senator Lugar says. He traces the upswing in approval for both the President and Republican senators to the fall in unemployment. Should the economic picture darken, he adds, ''it wouldn't make things easier'' in November.
The turn of the economy has put the Democrats, accustomed to domestic and public-welfare issues, into the uncharted waters of foreign policy and federal deficits.
How far those issues will take the Democrats is unclear. A dramatic turn involving US troops in Lebanon could have a big impact, as could increasing concerns that the $200 billion-plus federal budget deficit will cause higher interest rates for private loans.
The deficit is ''going to be a major campaign theme,'' says the Democratic committee's Mr. Atwood, but he adds that Democrats ''have to be very careful'' in handling the issue, which he says is casting a shadow over the recovery.
Meanwhile, ''social issues'' activists such as abortion foes hope 1984 will bring these subjects to the fore. The President gave them prominent mention as he launched his reelection bid. With the economy improved, the activists reason, the public might again focus on such issues.
One difference this year is that groups supporting ''choice'' on abortion are organized and ready for the elections, while leading abortion opponents, Sen. Jesse Helms (R) of North Carolina and ally Jepsen of Iowa, are among the endangered officeholders.
The abortion issue, which polls say moves a portion of the electorate, could be decisive in some close elections.
In Minnesota, for example, two Democrats are vying for the nomination to oppose Republican Sen. Rudy Boschwitz. The Democrats, Minnesota Secretary of State Joan Growe and US Rep. James L. Oberstar, are both liberals whose chief difference is that she favors legalized abortion, while he is an abortion foe.
Another new twist this year is the appearance of the ''he's too right-wing for our state'' charge. In 1978 the emerging New Right began knocking off a list of liberal Democratic senators, ranging from Dick Clark in Iowa to Frank Church of Idaho and Birch Bayh of Indiana. The charge in each case was that the incumbent was out of step with the folks back home.
Now challengers are trying that shoe on the other foot. North Carolina Gov. James B. Hunt Jr., who officially opened his Senate campaign last weekend, said in an interview that Senator Helms ''has not worked strong enough for an effective economy'' and that ''his agenda has been the social agenda.''
Governor Hunt, who studiously avoids subjects such as abortion, conceded that the social issues have ''some appeal in our state.'' But the governor argued he would better serve North Carolina. ''If I win, I will . . . work on the issues that really affect our people,'' he maintained. ''That is, more good jobs, a stronger education and skills training system in this country.'' The governor's popularity gave him an early lead in North Carolina polls, but Senator Helms's campaign has run a steady stream of advertising linking the moderate Hunt with presidential candidate Jesse Jackson and warning voters of the dangers of liberal Democrats retaking the Senate. The ads, financed with the aid of Helms's national fund-raising organization, apparently regained some of Helms's lost ground in the polls.
The Helms-Hunt race, dubbed the second most important of 1984, will likely determine whether a New Right senator can be ''too right'' for his voters, just as some Democrats during the '70s had moved too far left.
Similar tests are appearing in two other states. Rep. Tom Harkin (D) of Iowa, trying to unseat Senator Jepsen, said of the incumbent, ''His agenda has been the agenda of the New Right, not of Iowa.'' Jepsen counters that Representative Harkin, an unstinting progressive who has made a legislative mark in farm policy and human rights abroad, is outside the Iowa mainstream.
A third New Right politician, Sen. Gordon J. Humphrey (R) of New Hampshire, also faces a challenger from his left flank, Rep. Norman E. D'Amours, a moderate-to-liberal Democrat. Mr. Humphrey has already edged back toward the middle in an apparent attempt to shed a ''far right'' label, and he has received a boost from a rebounding New Hampshire economy.
Among the 33 Senate races this year, only a handful represent a serious challenge to the status quo in the upper chamber. First on almost any list are the North Carolina and Iowa contests. Until recent comebacks in polls, both Republican incumbents seemed doomed. At the least, the final vote count is expected to be close.
Other races of interest:
Texas. This most political of states has been embroiled in a political free-for-all ever since Senator Tower, one of the top Republicans, announced his departure.
Six major candidates have emerged, ranging from Rep. Ron Paul, a Republican whose conservatism is so extreme that he is the darling of the libertarians, to the liberal Democratic state Sen. Lloyd Doggett.
Front-runners include US Rep. Phil Gramm, a conservative Democrat turned Republican, and Robert Kruger, a moderate Democrat and former congressman who nearly upset Senator Tower in 1978. A May primary will determine the nominees for a race that will cost millions of dollars by the time a winner is named next November.
Illinois. Senator Percy had to fight for his political life when he ran for his third term six years ago, and he again faces problems, notably thin support even in his party.
In a recent interview, Illinois Senate minority leader Pete Philip, a Republican, said, ''I don't know what I'm going to do,'' when asked if he supports Percy. Percy's choices for US judgeships have been too liberal, he said.
Despite his leadership post as chairman of the Senate Foreign Relations Committee, Percy faces a primary opponent, GOP Rep. Tom Corcoran, who charges Percy has undercut the President. He has also exploited dissatisfaction in the Jewish community over Percy's stands on Israel. ''Chuck Percy says this man is a 'moderate,' '' charges a Corcoran campaign ad that pictures Yasser Arafat, leader of the Palestine Liberation Organization.
Senator Percy has countered with an endorsement from respected Jewish leader and former Sen. Jacob K. Javits (R) of New York and a pamphlet quoting President Reagan saying, ''I appreciate the support Chuck Percy has given me.''
But even if he wins the primary in March, Percy could face his first credible Democratic challenge in November. Rep. Paul Simon, the apparent front-runner in the four-man Democratic race, is given the best chance at defeating Percy. No matter who wins, the Democrat will probably hit Percy for supporting the President too much.
''It couldn't be helping me more,'' says Percy of the sniping from both sides. ''It pushes me right into the middle of the road,'' where he says he's always been most comfortable.
Tennessee. US Rep. Albert Gore Jr., a Democrat, has so solidified his lead in the race for Senator Baker's seat that it will be tough, if not impossible, to catch him.
The son of a former US senator from Tennessee, Mr. Gore has already raised $1 .75 million and has been busily wooing business people and conservatives to his side. Four Republicans have entered the race, with State Sen. Victor Ashe of Knoxville considered the early leader.
Massachusetts. When Sen. Paul E. Tsongas (D) announced that he would retire for health reasons, a gang of Democrats began throwing their hats into the ring. Among the candidates are US Reps. Edward J. Markey and James M. Shannon as well as Lt. Gov. John Kerry.
Republicans in this very Democratic state will have difficulty capturing the seat, although Ray Shamie, former Republican challenger to Sen. Edward M. Kennedy, has announced he will run, and there is speculation about former US Attorney Gen. Elliot L. Richardson.
West Virginia. The heir-apparent to the seat of retiring Sen. Jennings Randolph (D) is Gov. John D. Rockefeller IV, also a Democrat. So far the Republicans have failed to name a strong opponent, although they still hold out some hope for fielding former Gov. Arch A. Moore.
Other possible close races are little more than gleams in the eyes of challengers. Democrats hold out hope for GOP Sen. Rudy Boschwitz's Minnesota seat, especially with former Vice-President Walter Mondale, a Minnesotan, at the top of the Democratic ticket, attacting Democratic voters.
Sen. Lloyd Bentsen of Texas, chairman of the Democratic Senatorial Campaign Committee, has steadfastly held that no Democratic incumbent is vulnerable this year. Republicans, however, say they see some weakness in two states. They have convinced former astronaut Jack Lousma to challenge Sen. Carl Levin (D) in Michigan. Former Rep. Jim Dunn is also seeking the GOP nomination in Michigan.
The Republicans have also put Democratic Sen. Max Baucus of Montana on the vulnerable list, but the challenge has apparently motivated the incumbent into gearing up for his campaign early.
Most incumbents are going into the campaign from strong positions. Sen. Pete V. Domenici (R), for example, will be seeking reelection from overwhelmingly Democratic New Mexico, but a proud home state has watched its senator rise in the leadership to chairman of the Senate Budget Committee. His polling shows an approval rating of 89 percent.
Others who look strong include Sens. Nancy L. Kassebaum (R) of Kansas, Bill Bradley (D) of New Jersey, James A. McClure (R) of Idaho, and Sam Nunn (D) of Georgia, and Alan K. Simpson (R) of Wyoming.
Although 1984 promises some major clashes of ideas and candidate styles, some of the most spirited races will never occur because the principals didn't want to run. Doubts have surfaced about whether the prize, a seat in the Senate, is worth the effort and expense.
Prospects for adding new women or minorities look dim. Only four GOP women candidates four have decided to run, along with an equal number of Democratic women. All are long shots. Roland Burris, Illinois comptroller and a black, is a long shot for the Percy seat. Alabama Howell Heflin D Alaska Ted Stevens R Colorado William L. Armstrong R Delaware Joseph R. Biden Jr. D Georgia Sam Nunn D Idaho James A. McClure R Illinois Charles H. Percy R Iowa Roger W. Jepsen R Kansas Nancy L. Kassebaum R Kentucky Walter D. Huddleston D Louisiana J. Bennett Johnston D Maine William S. Cohen R Massachusetts Paul E. Tsongas* D Michigan Carl Levin D Minnesota Rudy Boschwitz R Missippi Thad Cochran R Montana Max Baucus D Nebraska J. James Exon D New Hampshire Gordon J. Humphrey R New Jersey Bill Bradley D New Mexico Pete V. Domenici R North Carolina Jesse Helms D Oklahoma David L. Boran D Oregon Mark O. Hatfield R Rhode Island Claiborne Pell D South Carolina Strom Thormond R South Dakota Larry Pressler R Tennessee Howard H. Baker Jr.* R Texas John Tower* R Virginia John W. Warner R West Virginia Jennings Randolph* D Wyoming Alan K. Simpson R