To Republicans he's the favorite target during elections, the archetype of the big-spending politician.
To Democrats he's the man so popular on Capitol Hill as to be unbeatable as Speaker of the House.
Friends describe him as a man of deep compassion for people.
A critic accuses him of ''cloaking himself in the garb of a crusader going off to do battle and seek the Holy Grail.''
And an admirer, spotting him in the car next to hers at a Washington stoplight, cheers him with, ''Congressman, keep up the good work.''
Almost everyone has some opinion of House Speaker Thomas P. O'Neill Jr., who after 29 years in Congress now finds himself more than ever in the national limelight. He has become the symbol of resistance against a Republican President who is almost his total opposite.
It would be hard to find a better match-up for President Reagan than Representative O'Neill of Massachusetts. Roughly the same age, they both come from Irish roots and share more than a touch of Irish charm. And each holds deep feelings about government.
That is where similarity ends, because ''Tip'' O'Neill believes that governments should help solve the problems of people, while ''Dutch'' Reagan holds that government is the problem.
''The truth is, his philosophy and mine are diametrically opposite,'' says O'Neill, explaining with a story that began at a Washington columnist's party.
A fellow guest told the speaker about a high school senior who ranked top in her class and had piled up other honors, too, but couldn't go to college. She had no parents and only social security for support, and the Reagan budget had wiped out her college benefits.
When O'Neill told the President, the speaker recalls, ''the President said, 'That's awful. Ed (Edwin Meese III, presidential counselor), let's see if we can take care of that girl.'
''I said, 'Mr. President, I'm not talking about a girl. I'm giving you an example. There's 42,000 of those out there every year.' ''
The son of a city politician in Cambridge, Mass., and grandson of an Irish immigrant, O'Neill would solve the problem by restoring benefits to all 42,000. Beginning in the Massachusetts State House where he sponsored a ''little New Deal,'' O'Neill has held public office almost since he was old enough to vote, and he makes no apologies for his record as a big spender.
''I look at it with pride in my heart at what I've accomplished,'' he says. Posted behind his chair in his private office at the Capitol are the words of Hubert H. Humphrey: ''The moral test of government is how it treats . . . the children . . . the aged . . . the sick, the needy, and the handicapped.''
Such a conviction, which O'Neill clearly holds with every fiber of his massive form, has catapulted him into the uncomfortable role of counter-president.
It's a 0osition the speaker does not relish. He's also at a decided disadvantage against Reagan, who not only has won in a national election but has spent most of his life communicating through mass media, especially on television. O'Neill's forte is talking with fellow congressmen, small groups, and his blue-collar Cambridge and Boston constituents.
O'Neill's huge size, his droopy, rumpled appearance, and his thick shock of unruly white hair may be an endearing plus in person. But on TV, a medium that magnifies without mercy while conveying little of the man's personal warmth, they become a liability.
O'Neill press aide Christopher Matthews blames news shows. ''TV tries to show him in combat with the President,'' complains Mr. Matthews, who says television depicts the O'Neill-Reagan bout as an old-time fight poster, with each fighter poised to punch. ''It's good for the ratings,'' says the aide, but not for the speaker, who frequently rises to the bait.
Last week O'Neill fired a zinger at the Republicans on their promise to save elderly,'' the speaker told a national television audience. The President, meanwhile, issued a soothing message from the White House Rose Garden that he would not reduce payments to pensioners.
For the most part, O'Neill has avoided extended TV exposure during the recent budget disputes. He sees himself as a ''scapegoat'' for Republicans who are having troubles among themselves over the budget. When the President gave his televised budget address, the Democrats sent Rep. Richard Bolling of Missouri to respond. The next morning's TV shows featured Congressman Bolling and majority leader Jim Wright of Texas giving the Democratic view. The speaker was unavailable, his office said.
However, the speaker continues to hold press briefings (without cameras) just before he goes to the House floor each day. The contact has won him a high degree of goodwill in a setting where he excels: face-to-face meetings.
If O'Neill has a main strength as a politician, it is his ability to deal with people on an individual basis. His long-held motto is ''all politics is local,'' and his idea of a good poll is walking down the street of his district. ''I go into the barber shop or talk to Vickie who runs the Italian food store, or go to the shoe shop man,'' he says. ''They will tell you their views.''
He has a politician's instinct for putting those around him at ease, usually by trying to find something he shares in common with them, or by telling a story.
With a handful of business representatives from Massachusetts last week, he compared golf notes (O'Neill is an avid, if poor, player), then launched into the story of his game with golf pro Sam Snead. Even with Snead as his partner, the speaker lost badly, but they had a good time anyway.
At the end of the day, Snead turned to O'Neill, ''O'Brien, you're a heck of a guy. What do you do for a living?''
His visitors laughed heartily and seemed to take no offense when the speaker good-naturedly informed them that he has always seen business groups such as theirs as the enemies of government.
O'Neill's support at home (he won 78 percent of the vote in 1980) has been matched by his personal popularity among his colleagues, a factor that paved the way to the speaker's chair. He continues to nourish it, and, even on his busiest days, will usually drop in on two or three fund-raising parties for Democratic members.
But popularity does not always translate into power on Capitol Hill, and O'Neill is facing the toughest test of his speakership not only from the Republican President, but from the sharp divisions in his own party. Democratic seats have declined steadily from a majority of 149 six years ago to a slim 51 margin today. With defections from ''boll weevil'' conservatives from the South , the party leadership no longer controls the House except in name.
''I have a party of conservatives, ultraconservatives, moderates, progressive liberals, and ultraliberals,'' says the speaker, putting himself in the ''progressive liberal'' category. During the key votes last year, O'Neill failed to rally the troops, and many voted with the Republicans.
The speaker has taken his share of criticism for the defeats, but he and others saw the Reagan budget and tax victories last year as unstoppable. Rep. David R. Obey (D) of Wisconsin, a liberal who has differed with O'Neill on tactics, says that the speaker ''could not have reversed what was happening last year.''
But Mr. Obey and other Democrats are unhappy that the speaker takes no action against turncoats such as Texas Democrat Phil Gramm who worked closely with the Reagan White House on the budget last year.
Even Rep. Richard Bolling, chairman of the powerful House Rules Committee and the speaker's ''right arm,'' takes O'Neill to task for going too easy on deserters. ''We pay too high a price to be chairmen and speakers when we keep people in the party who are really Republicans with a Southern accent,'' says Bolling. ''If they never vote for you, they're not worth keeping.''
O'Neill has flatly refused to take disciplinary action against errant Democrats.
''He has never been part of any threats of punishment,'' says Charles W. Stenholm, a Texas conservative who is coordinator for the boll weevil Democrats. ''He told us in our first meeting that he would never ask a member to go against his convictions or district.''
Still, Mr. Stenholm is far from satisfied with his party's leadership, which he says ignores conservatives. ''The speaker is a tad out of touch with the 17th District (of Texas),'' says Stenholm, making it clear that he would like to see a more conservative member, especially Budget Committee chairman James R. Jones (D) of Oklahoma, as speaker.
It is unlikely that anyone new will be occupying the speaker's chair next year. ''Tip would beat anybody who ran against him,'' says Representative Obey, echoing a general feeling on the Hill. ''That's the clearest indication you can find of bottom-line respect.''
''He's a very good speaker,'' says longtime colleague Bolling. ''And it's because of something fundamental in his nature: He has real compassion for people. He cares about people who are less fortunate that he is.''
Tip O'Neill may be a ''little too tough on Republicans,'' adds Bolling.
That's a statement that O'Neill's former chief adversary would second. Rep. John J. Rhodes, Republican leader from 1973 to 1981, has called O'Neill the most partisan person he knows. ''He doesn't believe in Republicans,'' quips the Arizona congressman.
''He has the instincts of an old-time politician,'' says Rhodes, ''that the name of the game is to win the next election. I guess that's not so bad if you believe winning the next election comes because you've done a better job.''
Assessing his own career, O'Neill lists as his accomplishments (1) playing an important role in stopping the Vietnam war (by coming out against it in 1967), ( 2) the ''money I've put in the budget for the future health of this country,'' ( 3) the Minute Man National Park at Cape Cod, and (4) his contribution to the economy of his home area.
As for the future, O'Neill will run for Congress next fall against Cambridge, Mass., Republican Frank McNamara, whose chief backing comes from Texas oil money.
The speaker has a lock-grip on his district, however. He still owns the modest wood-frame house at 26 Russell Street where he and his wife Mildred raised five children, just down the street from the house O'Neill was raised in. For the first 24 years of his congressional career, his family stayed in Massachusetts, and he commuted home weekends. Only since O'Neill became speaker has Mrs. O'Neill moved to Washington where they bought a condominium apartment in the suburbs for $92,500.
So sure of his own race is he that O'Neill had expected to spend this campaign year helping son, Lieutenant Gov. Thomas P. O'Neill III, run for governor of Massachusetts. But the younger O'Neill recently dropped out of that race.
Speculation that O'Neill would retire has been laid aside for now, but when he does quit, he will surely settle down with ''my Millie,'' as he calls his wife, at Cape Cod, Mass., where he owns a house conveniently near a golf course.
Meanwhile, he is said to enjoy his job as speaker and is bemused by his fame. Strangers frequently come up to him, saying, ''I know people must tell you this all the time, but you look just like Tip O'Neill.''
''I tell them, 'They sure do,' '' says the speaker.