In the last seven months, three ex-convicts have paraded through Congress to give the members lessons in leadership. They presented no formulas, no answers. They provoked huzzahs -- and uncomfortable questions in our officials: "How much am I willing to sacrifice?" and "Is it worth it?"

What Lech Walesa, Vaclav Havel and Nelson Mandela have in common, beyond conscience and conviction, is time spent in jail. That and the fact that they were caught up in causes larger than themselves.

"They are willing to die for what they believe," mused Sen. David L. Boren (D-Okla.), a super-cautious conservative and unlikely Mandela fan. "We're not willing to risk one bad poll."

Walesa and Havel spent shorter terms, but the circumstances were comparable. Walesa could have stopped organizing Solidarity. He chose not to. Havel, a playwright, could have gone along with the commissars in Czechoslovakia -- and a majority of his countrymen -- on human rights. He didn't.

And Mandela, because he held the anti-apartheid cause more dear than personal freedom, stayed in prison for 27 years, coming out, finally, on his own terms. He is, with his straight back and his straight talk, something of a miracle, and an argument for long incarceration. His incandescent quality was such that he got standing ovations all over. Even people who deplored his taste in allies, his anachronistic bent toward violence, were impressed.

All three forswore that most crippling of emotions, self-pity. None of them, in madly acclaimed joint session speeches, mentioned their suffering. A Democrat who voted against the flag-burning amendment or a Republican who swallowed George Bush's taxes, carries on more. Mayor Marion Barry, on trial for drug possession and perjury, sees himself as a martyr.

Walesa baited his captors. Havel said prison was the only place he could get any writing done. Mandela does not talk about his days on Robben Island; the man, at 71, is all tomorrow.

But members of his entourage who had talked with Mandela's fellow prisoners say that he led a structured, highly disciplined life, totally engaged as a college president and political organizer. A fitness fanatic, he got up at 3 a.m. to do calisthenics in his cell; relaying messages through the people who brought the food, he presided over unending seminars for fellow ANC inmates; drew up a curriculum for those, like so many blacks, deprived of education, and organized each cellblock under an ANC captain.

It isn't appearance that determines esteem. To be sure, Mandela, scion of a royal family, walks like a king, but Walesa is stocky and Havel is slight. Moral stature comes in all sizes.

Friends of the South African government have tried to rally the right to indignation over Mandela's singular preference in allies. "Yasser Arafat, Colonel Gadhafi, Fidel Castro, support our struggle to the hilt," he forthrightly replied.

"I wish he hadn't said that," says Boren, "but I can understand it -- you never turn your back on the people who were for you when nobody else was."

Boren, an ardent defender of the CIA, the agency said to have fingered Mandela for the South African police, made a trip to South Africa in 1989 and is the first to say he hasn't been the same since.

"It is one thing to see red-necked southern sheriffs in their inefficient way practicing discrimination, but in South Africa it is efficient and official. Meeting Albertina Sisulu {wife of then-jailed ANC leader Walter Sisulu} was "the single most radicalizing experience of my life."

Boren went to New York to greet Mandela and was struck by his "inner peace -- so rare in our system, especially in politics."

Is oratory the key? Probably not. Walesa, who came last November, had the House chamber rocking with enthusiasm for a real, live profile in courage, addressed the assemblage in a man-to-man manner, saying bluntly that Poland appreciated kind words but really needed money. Havel treated them to a literary masterpiece, an exquisite exposition of moral responsibility and Europe's determination to be a civilizing force again.

Mandela's luminous face set off a storm; the place was packed with people just palpitating to applaud. His accented English was somewhat hard to follow, and his speech was more conventional than, say, his beguiling rebuke to President Bush on the subject of ANC armed struggle the day before.

He spoke of the Constitution. It's what we have that our imported heroes don't. We have a peerless system of government that forbids the kind of oppression that they suffered. It may be why we don't really need heroes.