The new Democratic senator from Massachusetts strolled into the cavernous hearing room yesterday, a commanding presence of pride and satisfaction. He is the only freshman who won a seat on the prestigious Foreign Relations Committee, and as his eyes canvassed the room, you could almost see him replaying the drama of the decade past.

He was a witness before this same committee that April day in 1971, a brazen 27-year-old Vietnam war hero who had turned publicly against the same war that had earned him a Bronze Star, a Silver Star and three Purple Hearts. "How can you ask a man to be the last man to die for a mistake?" he demanded of the packed hearing room.

In his Army fatigues and ribbons, John Forbes Kerry seemed untouchable that day. And when he was done, Sen. Claiborne Pell (D-R.I.) spoke up.

"As the witness knows," he said, "I have a very high personal regard for him and hope, before his life ends, he will be a colleague of ours in this body."

Yesterday, at Kerry's first hearing, it was Pell who welcomed him back: "I remember a few years ago, he was a witness and I was hoping he would be joining us . . . And not only is he in this body, but on this committee."

But just as Pell had him marked for success, so his own impatience marked him for some failures. For years after his dramatic congressional debut, he would be accused by members of his own party of trying to leverage his wartime notoriety into political gain. It was a career of false starts at the polls for Kerry, though -- '70, '72, '80 -- and one that he wanted so much to pattern after that of his lifelong idol, John Fitzgerald Kennedy.

He even carried those same famous initials, which he unabashedly had monogrammed on his white shirts. Eventually, the joke was that the JFK stood for Just For Kerry. And when people described Kerry as "ambitious," it was nearly always pejorative.

"I know, I know," he says today. "I am not any more or less ambitious than anyone else in this business. I probably have been, in the past. But not recently, no . . . I think I got something of a rap 10 years ago which I brought on myself, partly because of my impatience and partly through my total focus, my absolute, total commitment to ending the war . . . I think there was an element of brashness . . . I admit that now . . . Why do people dwell on that so?"

Quipped a Boston Democrat recently when asked about Kerry: "Hasn't that guy left for Iowa yet?"

Today John Kerry is 41 and back in the Senate, a cocky, smooth operator with Gary Hart's aloofness and Ted Kennedy's ability to attract the cameras whenever he strides into a room.

In many ways, Kerry's success is a testament to the fact that a basically unpopular party player can overcome the odds and win. Days before the November general election, one headline on a Boston Globe opinion column proclaimed, "Just hold your nose and vote" for Kerry. Wrote the columnist, Mike Barnacle: "He looks like the kind of guy who wrote a game plan for life when he was still sitting in a sandbox."

Still, Kerry comes to the Senate with a certain cachet, projecting the same style that always seemed to place him on the fighting edge of success. And controversy.

He is handsome, and soon to be available, a divorce pending. He once tried to fly a plane under the Golden Gate Bridge but turned away at the last minute ("I could have continued under, I guess, but I opted out," he says), commanded his Navy patrol boat into enemy fire in the Mekong Delta, and as soon as he returned from Vietnam became the national coordinator of the premier veterans' antiwar group, Vietnam Veterans Against the War.

By 1972, his picture had appeared in every major news publication in the country.

"I'm tired of talking about myself," Kerry said one day recently, sitting on his office couch, legs propped on a coffee table. "Knowing what I know about this city and the process, the more you tell me those are the perceptions of me -- dashing, flashy -- the more I say I have to be careful . . . The French philosopher Andre' Gide's response to people trying to classify him was 'don't try to understand me too quickly.' . . .

"Somebody sees me walking down the hall, and sees that I'm 6 foot, 3 1/2 inches tall, and thin, and, you know, they have a perception. They say, 'This guy is this way,' and then the stereotypes develop . . . A lot of people who criticize me today -- and I think it's the residual from back then -- I say they just don't know me."

He talks with Boston lockjaw, at times barely moving his lips. If you close your eyes, the cadences are remarkably familiar. As is his career history: enlisting in the Navy and becoming a naval officer, running for Congress upon his return, and even dating one of Jacqueline Kennedy's half-sisters. And now the Senate. Recalls a classmate at Yale, where he was an undergraduate, "When John was around, we'd always say, 'Here comes little JFK.' " Even People magazine asked him recently if he did anything special to make his hair look like Kennedy's. He doesn't.

"I've worn my hair the same way since I was three," he says. "And my initials were JFK in 1943 -- when I was born, before Kennedy had even gone to fight in the war. I didn't have anything to say about it, folks. Please. It's just a lot of bunk!"

Says Cameron Kerry, a younger brother: "Anyone interested in politics from that era was affected by Kennedy. When you're an impressionable kid, the situation is certainly magnified when you wake up to the fact that you have the same initials."

Kerry was born in Denver and raised predominantly overseas, his father a foreign service officer, his mother a Forbes, one of New England's oldest blue-blood families. He was brought up a Catholic, although his Irish-Catholic lineage is snidely dismissed by cynical Boston pols.

"He is more a Forbes than a Kerry," says one almost disdainfully.

Even those who like Kerry agree.

"This is not an Irish family," says friend David Thorne, whose twin sister is Kerry's estranged wife, Julia. "To understand John, you have to understand his family. They are a very reserved New England Anglo family which does not express emotions. John is a difficult person to get close to. He's remote and not very good on a human level. He's not very good at assuaging feelings. I think he's gotten much better . . ."

Kerry says today that in fact he does take his personal relationships more seriously than when he was younger. He is the attentive father of two girls, Alexandra, 11, and Vanessa, 8, who live in Boston with their mother, and his friends say that his wife's request for the separation in 1982 after 13 years of marriage devastated him but ultimately changed him for the better.

"I think you bang your head against brick walls, and either one of two things happens," he says. "You either knock yourself senseless or you grow. I think I am a sensitive person . . ."

Those close to him say he dates but that he really would like to see his marriage reconciled. He refuses to discuss the subject, saying only, "It's too complicated to explain . . . We are really close friends and we're separated, and that's the way it is right now."

John Kerry has spent the last decade paying the dues that seemed so unnecessary years earlier.

He is an attorney now, having enrolled in Boston College Law School soon after his 1972 congressional defeat. In the ensuing years he worked in the Middlesex County district attorney's office as the first assistant, prosecuting a major organized crime figure, and he is credited with reducing the backlog of cases from 11,000 to about 250. He was in private practice for a while, invested in a cookie business, of which he still retains a small interest, and in 1982 achieved his first elected office, becoming lieutenant governor of Massachusetts under Gov. Michael Dukakis.

The reviews were fairly positive. Yet there is still something about him that makes other politicians uneasy.

Before running for Congress in 1972, he did some highly publicized "district shopping." He purchased a house in Worcester, 40 miles west of his home, in order to run for Congress there. But he never moved there. When another seat became available in Lowell, he ran there instead, claiming his parents' residence as his own. "It was insurance," he says. "That's part of the brash series of things I refer to, it was that period of time. I was totally consumed with the notion of going to Congress . . ."

The surgery to have the jawbone adjusted on his long, oval face did not go unnoticed, either. It was performed, he says, to correct damage done during a hockey accident. Others point out that the operation coincidentally made him more attractive to the cameras.

Some criticized him for being unpatriotic when he made a flamboyant show during a Washington war protest of throwing his medals away. When, last year, he acknowledged that he had discarded someone else's, he was crucified for being a hypocrite.

"It's such a personal thing," he says. "They're my medals. I'll do what I want with them. And there shouldn't be any expectations about them. It shouldn't be a measurement of anything. People say, 'You didn't throw you medals away.' Who said I had to? And why should I? It's my business. I did not want to throw my medals away."

Insiders say he's downright disrespectful. Two weeks before the general election, he spurned House Speaker Tip O'Neill's offer to campaign for him, abruptly canceling a trip they had planned for the Speaker. Kerry's office maintains it was a logistics problem. O'Neill is said to have been furious.

"He has time to work at these relationships now, and sure, he will," says Ron Rosenblith, his top political aide and administrative assistant. "I'm much more concerned about what the voters think, than the insiders. How much does he really want to change? The reality of the situation is he's here. He won."

And Kerry supporters maintain that all along he has been learning the hard lessons.

"People choose to forget that John pulled out when I ran because he thought it was better for the party," Rep. Barney Frank (D-Mass.) says of a 1980 congressional race. "He had as good a chance as any . . . I only won with 4 percent of the vote."

Supporters also say he is a victim of the stereotypes that dog him. Many of those interviewed who worked with him in the Dukakis administration, for example, said they had been pleasantly surprised.

"Many of us who didn't know him before feared this was an upstart lieutenant governor who would make it difficult for us to make policy by publicly opposing our efforts," says Frank Keefe, Massachusetts secretary of administration and finance. "Those fears ended up being unfounded during the first week, when he stayed to all hours of the night trying to work out a budget compromise."

So perhaps Kerry is a man whose time has finally come. When Sen. Paul Tsongas announced his plans to resign due to illness, Rosenblith immediately tracked Kerry down in Brussels.

"I had just woken up and Ron said 'Are you lying down?' " recalls Kerry.

"I really felt awful for Paul," he says. "I was genuinely sick about it all day . . . And then I began to think about it, and I put it out my mind for about five days . . . I felt in my gut I should run."

John Kerry has only been here a month, but he exudes a certain confidence not often seen in first-term Senators. He has already purchased a $180,000 town house two blocks from his office on Capitol Hill.

On the social circuit, he is already a presence, gushed over at various party stops. Last December, before he was even sworn in, Kerry drew a crowd at a black-tie party at the National Portrait Gallery.

"Is he married?" a woman asked, as the cameras flashed around him, a question that's been asked all over town.

On the Senate floor, he projects the attitude of an insider. And when dealing with constituents he makes it seem as though he has been a senator forever.

In the course of three interviews, he has displayed the finesse of a political pro, answering all the questions, but never saying too much, or the wrong thing. He's polite, but reserved.

He says he doesn't like the publicity.

"When I was 27 years old, two days before my testimony before the foreign relations committee everyone was writing about my putative run for the White House. It's the worst thing in the world you could have written. I don't want that stuff. I don't seek it. I cringe as a matter of fact."

Old friends say Kerry was fascinated by public office early.

"I don't really know when the first moment was," he says. "I remember when we were in Washington in 1952 -- I remember my sister was really active. She was raising money for Adlai Stevenson, and I went out and tried to raise money door-to-door, and we went and raised five bucks or something."

He attended the exclusive St. Paul's prep school in Concord, N.H., where political posters adorned his dorm room and he argued politics with classmates late into the night. Two years before his graduation, Kennedy was elected to the presidency.

"That was a real catalyst," he says. "He kind of touched chords for all of us."

In 1962, Kerry hit Yale running, displaying the same kind of singlemindedness that would follow him for two decades.

"John was unusually active for a freshman," says Sen. David Boren (D-Okla.), who met Kerry through Yale's Political Union, a well-known debating outlet for politically active students. "He ran for a union office and won, which is rare for a freshman, though not unheard of. I suppose some people thought him to be arrogant -- he was certainly not a silent freshman. I always thought of him as intense, more of a go-getter. Knowing him then, I am not surprised to see him in the Senate."

Boren, three years ahead of Kerry in school, said he later wrote a letter of support when Kerry was invited to join Yale's Skull and Bones Society, the oldest and most prestigious secret society on campus.

By 1966, the Vietnam war was near its peak. Like so many others of his age, it was either enlist or wait to be drafted. He enlisted.

"Oh, it was a major, major formative experience in my life," he says of his tour there. "The whole thing was just critical to me. When I came back from Vietnam and had a very traditional position as aide to an admiral, uhmm, it was with a lot of basic commitment to ending that war, that led me to say, 'I've got to get out of here.' "

Vietnam became a touchstone for John Kerry's political career. His critics say he protested when it was in vogue to do so and, during the campaign 12 years later, emphasizing his war citations, running ads that showed him marching through the rice paddies.

"It's not contradictory in the least," he says. "It is absolutely, 100 percent consistent. I went because I believed in this country, because I owed it to myself and the things I stood for. So I went. And when I got there I changed."

Then-lieutenant Kerry, a commander of fast patrol boats, soon distinguished himself with an impressive combat record.

According to the presidential citation for the Bronze Star he received, once when he "discovered he had a man overboard, he returned up the river to assist. The man was receiving sniper fire from both banks, Lt. Kerry directed his gunners to provide suppressing fire, while from an exposed position on the bow, his arm bleeding and in pain, with disregard for his personal safety, he pulled the man aboard . . . "

When Kerry returned he mobilized 5,000 veterans on the Mall to protest the war. After his testimony to the Foreign Relations Committee, according to The Boston Globe, Kerry registered 6 percent ahead of Abe Beame in a New York City public opinion poll on mayoral candidate preference.

When Kerry ran for Congress one year later, Richard Nixon was obsessed with him. As the story goes, Nixon, already comfortable in his landslide victory over George McGovern, would not go to bed on election night until the results of Massachusetts' fifth congressional district were tallied, and Kerry was pronounced the loser by 18,000 votes.

But his Vietnam experiences would bring him as much grief as fame. During his senatorial run, he came under fire from all sides.

In the primary, a group of Massachusetts Vietnam veterans endorsed former congressman James Shannon, the Democratic establishment's favorite, after Kerry appeared in an ad standing before the Vietnam Memorial in Washington. "The ad made it seem as though 57,000 names on the wall were endorsing him," said Richard Ducey of the Vietnam Veteran Leadership, who supported Kerry in the general election but not the primary.

The lowest moment of the general election came when the John Birch Society and Maj. Gen. George S. Patton Jr., son of the famous general, charged that Kerry was a communist sympathizer guilty of "near treasonous activity" in opposing the war. In the end, this worked against his opponent, businessman Ray Shamie, whom he beat with 56 percent of the vote.

And what exactly makes a hero? he is asked.

"Basically," says Kerry, "you don't get killed."

When yesterday's Foreign Relations Committee hearing adjourned, Kerry was asked about his return to the committee, in light of his current interest in foreign affairs. He has often paralleled the U.S. role in Central America, as well as the arms race, with the country's early involvement in Vietnam.

"It was strange being there," he said. And then, referring to a witness who had just defended Star Wars, the antimissile defense system, by calling it "the light at the end of the tunnel," Kerry smiled: "I walked in and I knew I had been there before, and when he said 'the light at the end of the tunnel,' my blood went bubble, bubble, bubble. That's what they used to say about Vietnam. And I knew I had been there before."