Nineteen months into the Reagan revolution, Tip O'Neill has no regrets. "I wouldn't have changed a damn thing," he insists. "Not one thing. Everything went on schedule. Exactly."

The venerable Speaker of the House, most powerful Democrat in the country, says he thinks of himself as "Horatio at the bridge."

Leaning back in a leather chair in his chandeliered office, he cannot resist an I-told-you-so grin.

"I was the only voice that was really criticizing them," he said. "I kept hammering away and hammering away and hammering away. A lot of my people were running away, frightened of 'em, scared stiff of 'em. And I always figured that -- listen, I'm an American. I hope that it'll work, like everybody hopes that it'll work. But you know in your heart, and you know in your mind and you know from experience that no way is it going to work."

There is a touch of euphoria among Democrats these October days. They won a few votes in the waning days before the congressional recess. Polls on next month's elections are looking reasonably good. The unemployment rate hit double digits in September, and Democrats can argue that it is not their fault.

Election-year optimism has spurred a bit of revisionist political science. The fear and confusion of 1981 is half-forgotten, and defeats of the last two years are attributed to a grand strategy. And, now that things appear to be looking up, Thomas P. (Tip) O'Neill Jr. of Massachusetts, once everybody's favorite scapegoat, does not look so bad anymore.

"If Reaganomics had worked, the drumbeat on Tip would have continued," said Rep. Tony Coelho (Calif.), chairman of the Democratic Congressional Campaign Committee. "But Tip has come out of this confrontation with the president as a folk hero for the Democrats.

"The White House thought they would beat the heck out of him. Reagan comes across as very smooth, hair always neat, very expensive clothes. Tip comes across as very American. His shirt is rumpled. He doesn't always have his hair combed. He isn't the movie star. He's the guy next door.

"The Republicans thought they would take Mr. Smooth and Tip and show Tip as the old pol. But nowadays, I think people kind of like that old pol. They sense he's a fighter."

Ah, short memories. Only last year, headlines proclaimed the Democrats in disarray, reeling from Reagan's spectacular victories on the budget and tax bills. "Repeal O'Neill" buttons sprouted around Capitol Hill. The Speaker's flock was downcast, grumbling that, at 68, Tip was old, tired, out of touch. Some called for his resignation.

Rep. Les Aspin (D-Wis.) wrote constituents: "Tip O'Neill is a good friend of mine . . . a lovable old bear . . . . But now, I regret to say, Tip is reeling on the ropes. Tip grew up in the Depression. His politics have always been straight New Deal. In 1981, the New Deal doesn't carry a lot of water. Tip doesn't understand the explosions that have been going off since November. He's in a fog."

Today, the critics are becalmed. The Speaker's relentless blasts at the Reagan program, issued almost daily as the press gathered around his large leather-topped desk before the opening of the House, set a motif for the 1982 campaign: fair vs. unfair, rich vs. poor and working class, "them" vs. "us."

He beat the White House on the veto of the supplemental budget last month, then outfoxed it on the balanced budget amendment by whisking the bill to the floor before Republicans could marshal their forces.

O'Neill's verbal fumbling has been the butt of jokes. During the tax-cut fight, he called Rep. Barber B. Conable Jr. (R-N.Y.), a Ways and Means Committee member, "Barnable." But in floor debates this year, as when he recounted in the nuclear freeze fight his witnessing of an atomic blast 30 years ago, the Speaker's eloquence has stilled the raucous chamber.

"The first year was a hard year, no question about it," O'Neill said in a interview in his high-ceilinged, antique-filled office last week. "A lot of the younger fellows didn't think we had a program or a plan. We had a plan every inch of the way, and the plan was to win the final ball game. Come in in the fourth quarter and, when the final score was tacked up on the first Tuesday in November, we would be the winner."

Nicknamed for a baseball player who often hit so many foul tips that pitchers walked him, O'Neill relishes the partisan sport of politics. With his imposing size, his 10-inch cigar, his shock of white hair, bulbous nose and twinkling blue eyes, he is caricatured as the Boston Irish politician. That he is, and he is proud of it.

But in person, there is a dignity in his charm, an authority in his demeanor and a gentleness behind the shrewdness that explains how the grandson of a brickworker from County Cork became Speaker of the House.

Q: What's Reagan like to deal with personally?

A: He's the most unbelievable man I have ever met in my life. You know, I repeat this story: 'Tip, my program's working out there. You know, Ihaven't hurt a soul. Do you know I put 350,000 new jobs in America since I became president?'

I said, 'Mr. President, you know there's 10 1/2 million people unemployed out there. Of course your program isn't working. Number two, how do you cut the budget $42 billion and $17 billion this year without hurting people? And number three, Mr. President, you've said this to me before. Gee, I'm amazed that you say it again. We ought to be creating 3 1/2 million new jobs a year.'

Q: This is a one-on-one conversation?

A: This is a one-on-one conversation. Then he'd say to me, 'Did I ever tell you the story of Murphy the spy?' And he'd tell you an Irish story. Now I'm telling you, this fellow's absolutely unbelievable.

And he says to me, 'Hey, you know, Tip, we agreed after five o'clock or six o'clock we're going to be friends.' Certainly we're friends. I don't have any enemies in public life. That's what I love about a democracy. That's what I love about the Congress . . . .

In the opening months of the 97th Congress, O'Neill received an average of 58,000 letters each week in favor of Reagan's program. "I had problems with some of my own people, saying frustrate 'em, don't allow these programs to come to the floor," O'Neill recalled. "On the budget, we had alternatives , but it was obvious that none of them were going to win. Whatever Reagan had at that particular time, he was going to win and he did win overwhelmingly."

Yet even as the Reagan tidal wave washed through Congress, O'Neill was telling the pundits, "The horse that runs fast doesn't always run long."

Looking back on it, he says, "I'd seen it happen before. No question in my mind from the time of Hoover and McKinley, even back to Plato during the Greek democracy, trickle-down theory -- their economic theory -- it didn't work then, and it wasn't going to work now. And it was obvious that you can't take $1.6 billion and have it for five years in defenses and give $800 million back to the rich."

So the Speaker put Reagan's program on a fast track, albeit with a few procedural and substantive challenges along the way and, by August, 1981, it was in place. "We were fighting an opposition that was supremely confident that they were doing the right thing and so proud of their victories that they couldn't conceive that what they were doing was wrong and that disaster was ahead of them," he said.

Now O'Neill is predicting a 14-seat Democratic gain in the Nov. 2 general election, and even the restless younger Democrats are praising "the strategy" of letting Republicans have their head so they will fall on their faces.

Rep. Albert Gore Jr. (D-Tenn.) calls it "rope-a-dope." Muhammad Ali, he explains, "would put his gloves in front of his face, stay on the ropes and let his opponent hit him as much as he wanted. Then when the opponent got tired, Ali would close in for the kill."

"The Democrats had a difficult time in 1981 realizing we were the party out of power," Rep. Henry A. Waxman (D-Calif.) said. "At first, we tried to make compromises instead of articulating our position and focusing the issues for a national debate. We tried to imitate the Republicans on the 1981 tax bill. But we learned from the experience of losing without looking honorable.

"Now Tip's message that the Reagan program is unfair is coming through. There's a growing respect for Tip as chief spokesman for the Democrats."

Nonetheless, the Democrats have used other spokesmen to respond to the president's television speeches, perhaps in part because O'Neill's image might contrast unfavorably with Reagan's on the air.

In 1980, Republicans had attacked the Speaker in an ad featuring a fat, white-haired actor whose car ran out of gas on the highway. Last year, Time magazine likened his 6-foot-2-inch, 260-pound torso to "a giant plum pudding."

"Tip is a perfect target for our candidates," says Rep. Guy Vander Jagt (R-Mich.), chairman of the National Republican Congressional Committee. "In my speeches, I always ask, 'Do you want to leave the machinery of the House in the hands of Tip O'Neill and his liberal philosophy?' A number of Republican candidates would pay Tip's expenses if he'd come in their districts to campaign for their opponents."

O'Neill's opponent this year, a young Boston lawyer, is handing out running shirts bearing the slogan: "Get the Fat Out of Government."

Q: Did that Republican ad affect you personally? People were saying you were big and fat.

A: Hey, I'm jovial! Everybody loves a fat man. Let me tell you something. There are more people out there trying to lose weight than there are trying to put weight on. Why do you think there's so many joggers out there?

Q: Some people like the idea of having a slim, trim -- your image is sort of the old pol.

A: Well, you get everybody in the Reagan administration all slim and trim from the president and the vice president. They had a golf game out on one of the local golf courses the other day. Four Cabinet members played golf, and there were 32 Secret Service agents taking care of them in all types of carts. And look at me. A big jovial guy. I have nobody protecting me. Just lovable Tip, that's all.

Q: Seriously, what about your image as a spokesman for the Democratic Party?

A: I looked at myself as kind of Horatio at the bridge. Somebody had to stand out there and stay with the basic creed of the Democratic Party, the concern for the needy and the handicapped and the golden ager. Somebody had to speak out and stop being an apologist as many in our party were.

I never apologized for anything we did out there. We did the right thing.

The president likes to talk about the misspending of the last 30 years. He doesn't understand the last 30 years because he's been a man of wealth. Successful. By luck.

God gave him a handsome face and a beautiful voice. God didn't give that to everybody, and there has to be people out there protecting those people. And now it's the Democratic Party.

When there were those who ran, I didn't run. I stood my ground, and I fought the fight . . . I can't walk down the street . . . I can't drive in the car without people standing there: 'Tip, thank God we have you.' You ought to see my letters from all over America . . . .

To be sure, some wish the strategy were less negative. "Tip's ingrown in his political style," says Rep. Bob Edgar (D-Pa.). "For its time, it was a good style. But this would have been the time to push imaginative ideas and build coalitions with moderate Republicans. Instead, we make a caricature of ourselves with a billion-dollar leaf-raking jobs bill. We put forward tax and budget bills as bad as the Republicans.' "

O'Neill bristles at the suggestion that the Democrats were on the defensive. "What have we accomplished?" he asks. "We've saved Social Security. We've saved the programs for the handicapped. We've stopped 'em from lacerating education programs. We just passed a job training bill. The 1982 tax bill."

As for new ideas, he growls, "Let's not go through that again. The Republicans control the Senate. They control the White House. The obligation is on them . . . .

"There's 13 million unemployed Americans. The senior citizen is living in fear . . . for his Social Security. You're not going to sell fresh new ideas for the future when things like that are happening. But we are putting our house in order. We're ready to take over in 1984, and we'll have programs."

What those programs will be is a struggle among the many factions of the Democratic Party, liberals and neo-liberals, moderates and conservatives and neo-conservatives.

At a breakfast with reporters early in 1981, O'Neill confessed, "I've been one of the big spenders of all time," and went on to boast how, without any publicized amendments, he had personally inserted into the budget at different times $160 million for breast cancer research, $45 million for research that helped increase the average height of dwarfs from 26 inches to 50 inches, $18 million for knock-kneed children and $12 million for children with turned-in ankles.

Then, with the Reagan landslide fresh in his mind, he reflected, "This is a new ball game now . . . . Programs like these are going to die on the vine. But that doesn't mean that what we have done over the years wasn't right."

Today, O'Neill is adjusting to the change. He defends the past: "In the '30s, 50 percent of America was impoverished. Today 10 percent of America is impoverished. The golden agers -- 65 percent of them were impoverished, and today only 14 percent is impoverished.

"Only four out of every 10 high school graduates in the '30s went to college, and 65 percent do now . . . . We went through the era of all these programs because we were developing a middle-class America."

But O'Neill accepts a different future: "Middle-class America is out there now. Democrats will never go back to the old theories as we went through them. The '80s are a period of smaller automobiles, smaller homes, less government.

"You see what has happened to energy, how we've cut down from 18 million barrels of oil a day to 14 or less. America is contracting itself. America wants less government and less regulation, and there's no question that there will be more of an input to the Democratic Party with business than ever before."

Q: What kind of Speaker are you?

A: I have a complete open-door style. Sam Rayburn, he wouldn't know 20 members of his own party other than the committee chairmen. He knew nobody on the other side of the aisle. If you wanted to come in and see Sam, you made an appointment two or three weeks in advance.

I can have the mightiest of business people out there and, if a member of Congress comes in, he comes in. I talk over their legislative problems, their personal problems, their political problems. I operate with more ad hoc committees. I have more meetings of the policy committee and the steering committee and the caucuses. Sam used to believe in one caucus a year to elect the Speaker.

Q: Some of the younger members say you're getting tired.

A: There's nobody that has the all-around knowledge of everything that's going on that I do . . . . How do you think I got to the leadership? I was on the Rules Committee. I wasn't an expert on any one thing. But . . . I knew how legislation affected people at home. I'd know whose philosophy it was helping and whose philosophy it was hurting. I'd know whether it was good for the businessman or bad for the businessman. And I've been able to count the House along the line.

So I do my homework. If somebody were to say to me on a specific issue or one particular thing -- no question people in a debate could take me apart. But as far as the overall operation, the overall legislation that's pending, what it'll do to the country, I don't take my hat off to anybody.

Rumors sweep through the Capitol with regularity that O'Neill will retire this year. Or that he will retire in 1984. Or that he will step down as Speaker but continue as a Massachusetts congressman. Would-be successors are positioning themselves: Reps. James C. Wright Jr. (Tex.), Dan Rostenkowski (Ill.), Thomas S. Foley (Wash.), James R. Jones (Okla.).

"This is what I fear most," said Rep. David R. Obey (D-Wis.). "The session before Carl Albert retired was a disaster. As good as it looks now, we could screw up the next election.

"Politicians only have so much energy. Either it's directed at planning step by step for what Reagan is going to toss at us, or we destroy ourselves with four or five campaigns for Speaker, Majority Leader, Budget Committee chairman -- none of which are more than a footnote in history. We don't need a lame-duck Speaker. The best thing Tip O'Neill can do is to say very strongly that he expects to stay for six more years."

So how much longer does he want to be Speaker? O'Neill is asked. The red-carpeted room is quiet as the afternoon sun spills through the brocade curtains.

Finally, he says, "I will know. My political insight will tell me the proper time to pull the shades and depart from the scene. When twilight arrives, I will know."