It's long been assumed that any truly ambitious politician would die to be president. Sen. Joe Biden, D-Del., almost did.

Nineteen months after national humiliation, and 14 months after he almost lost his life, the youngest man elected to the Senate in 150 years, at age 29 in 1972, has a new lease on - and attitude about - life.Biden credits the change to his running for president.

"Now that I've survived it unscathed," Biden says as he knocks on the wooden table in his office, "it's been the best year of my life in the sense I've learned more about me. I've learned what I can take and do."

Two years ago Biden seemed likely to be the Democratic nominee in 1988 after Gary Hart went down in flames: He was articulate and attractive to women voters; he could raise large amounts of money, and he seemed marketable as a moderate in a party that badly needed one.

But on Sept. 12, 1987, just before he would chair the highly-publicized Senate confirmation hearings on Supreme Court nominee Robert Bork, it all began tumbling down for Biden.

In short order, Biden conceded that at times he had used a British politician's campaign speech without giving credit, and he was embarrassed over exagerrating his law school record and by a law school incident that caused him to repeat a course because of questions about plagiarism.

Biden dropped out of the race, saying the Bork nomination needed his undivided attention. If Biden was bitter, he kept it well hidden.

"Everyone was marveling at his comportment in the hearing room," said a former Judiciary Committee staffer during the Bork hearings. "In the back room of the hearings he went out of his way to be gracious. But . . . he made various comments which made it clear to anyone listening that he felt a tremendous amount of pain and anger."

Once the hearings were over, Biden dropped from public view. And on Feb. 11 - five days before the New Hampshire primary - Biden underwent high-risk surgery to correct a life-threatening aneurysm in his brain.

It now turns out that Biden, before he withdrew from the race, was close to a political breakout that could have propelled him out of the pack and eventually into the Democratic presidential nomination.

Joe Trippi, then deputy campaign manager for Rep. Richard Gephardt, D-Mo., confirms their internal polls at that point showed Biden in front with the momentum to win Iowa going away.

Sources in Massachusetts Gov. Michael Dukakis' camp - whose aides leaked the story about Biden's speech plagiarism - say their polls showed the same.

Iowa State Democratic Chair Bonnie Campbell in late summer began telling people privately that Biden had suddenly, clearly moved to the fore in her state.

In retrospect, however, it seems that if the scandal hadn't gotten him, the aneurysm would.

Valerie Biden Owens, his sister and campaign chairman, recalls that "When he withdrew, no one saw it as a blessing. None of us were jubilant. It was a sad time. I was angry."

In hindsight, she says, the withdrawal "was a blessing." Had he not withdrawn, "the doctors have led us to believe he would be dead."

Biden had already ignored previous warning pains - assuming it was just a back problem - and his traveling aide routinely carried a large bottle of extra-strength Tylenol for him.

Biden says he would have ignored the symptoms even longer if he had been in the heat of the campaign:

"My guess is I would have not quit. I would have tried everything I could. Whether or not it would have gotten so bad that there's nothing I could do about it, I don't know. My guess is I would have tried for 24 hours, and if (the doctors) are right about what happened in those 24 hours, I would have been gone anyway."

As it was, doctors at Walter Reed Hospital in Washington thought he was so close to death that they rushed the surgery before a second doctor they wanted on hand could get there.

Biden subsequently had two more major operations and spent months recuperating before returning to the Senate last fall.

He has plunged back into the Senate with zeal, trying to erase any doubts about his abilities that past embarrassments may have caused. He plans to run for re-election to the Senate next year, and he's considered a safe bet. He remains chairman of the Judiciary Committee and a senior member of the Foreign Relations Committee.

It's clear from watching Biden - who still commutes daily by train from his Wilmington, Del., home to Washington - that the presidency is still in his sights. He has ruled out a 1992 race, but associates think he's on a timetable for 1996.

"I have a great deal more patience," says Biden, once known in Washington as a young man in a hurry. But, he adds, "Don't get me wrong - I still haven't become Job.

"I am no less ambitious in terms of my dreams for my family, myself and my country, but I am much less anxious, much less hurried. . . . For me it was always the next stop. I never took the time, other than as it related to my family, to say, `I like what I'm doing.'

"I can make a real contribution, and when I feel the time is right, I'll move."