JUST two weeks have passed since the Democrats' stunning Senate victory in Pennsylvania, but in the nation's capital, much has changed.The Pennsylvania vote, fueled by middle-class anger over the loss of jobs, jolted the White House. President Bush, who had soared over the political landscape like an eagle just six months ago, suddenly finds himself back on the ground fighting with Democrats over political scraps. After ignoring the serious recession at home to concentrate on problems abroad, Bush now seems to be losing control of the political agenda. Democrats are hammering him on health care, middle-class taxes, and the economy. There's even flak from Republicans. Conservative Pat Buchanan will apparently challenge the president in the New Hampshire primary by demanding cuts in foreign aid, by criticizing illegal immigration, and by pointing out that Bush reneged on his "no new taxes" pledge. Horace Busby, a long-term observer of the presidency, says there is "great significance" in all of this, especially in Mr. Bush's recent flip-flop on top Democratic priorities: the civil rights bill and extension of unemployment benefits. "The Democrats on Capitol Hill have taken over government policy," Mr. Busby says. The White House, he says, is "in retreat." The Washington Post, in an editorial, agrees. "[Bush] is looking for someone else on whom to lay the blame," the Post says. "He has recently tried to put the villain's mustache on the Democratic Congress, the Fed, and even, for its failure to consume enough, the public." The Post concludes: "He needs another adviser." Ginny Terzano, an official at the Democratic National Committee, says Pennsylvania put the "stamp of approval" on Democrats' top 1992 presidential campaign issues, jobs and health care, and "opened the press corps' eyes" to the power of the Democratic message. In Pennsylvania, Democrat Harris Wofford upset former Attorney General Dick Thornburgh (R) by nearly some 340,000 votes. She continues: "Not only is George Bush caving in on many of the Democratic-sponsored pieces of legislation, but he is caving in for a simple reason: He doesn't have a plan of his own." Analysts say that if the economy suddenly rallied, most of Bush's problems would probably vanish. But that isn't happening. Jobless claims rose to 454,000 in the week ended Nov. 2, the highest level since May. Auto sales are dismal. Retail sales of clothing and other nondurables are flat. The stock market is gyrating nervously. The economy, as one expert puts it, is "punk." With windows rattling in the Oval Office, events have moved swiftly in Washington. Taken together, they form a troubling mosaic for Bush. Among the reports since the Pennsylvania vote: * Bush cancels his two-week Asian trip to concentrate on domestic issues. * The Federal Reserve, at White House urging, slashes the discount rate by 0.5 percent to stimulate the economy. * Bush calls for credit card companies to lower their interest rates to stimulate spending. * The stock market falls 120.31 points, or 3.9 percent, on Nov. 15, in part because of fear that new federal rules will be imposed on credit cards. * Republican lawmakers call for a $150 billion, five-year program to bring health care to most of the 34 million Americans who have no health insurance. * Republican and Democratic lawmakers protest plans to divert $1 billion to humanitarian aid for the Soviet Union and insist that the money be spent for relief at home. * Bush puts aside his objections to "quotas" and signs a civil rights bill, thereby angering many right-wing Republicans. * Bush reverses himself and supports new unemployment benefits for approximately 3 million Americans whose payments have run out. * Reports surface that White House aides are worried that a proposed free-trade treaty with Mexico could backfire against Bush if Democrats charge that it will cost US jobs. * White House advisers wrangle in public over domestic policy, particularly about the need to act strongly on the economy. * Bush tells aides that he wants his reelection campaign team orgnized by December instead of January, as planned. "Bush is on the defensive non-stop," says Terzano. The most convincing proof that the White House is in "economic disarray," she says, is that "he is not offering alternatives" to Democratic plans. Busby, who once served as secretary to the Cabinet for President Lyndon Johnson and now writes "The Busby Papers," says Democrats should be cautious about offering too many programs, however. Let the White House try to lead, he suggests. One reason: When Democrats propose new programs, Republicans can hang the "big spender" tag on them. A number of analysts suggest time now favors the Democrats. Most Americans (70 percent, according to the latest poll by the Wirthlin Group) believe the country is on the wrong track. Bush's support could be dragged even lower in coming weeks, they say.