David Frost badgered statesmen and made small talk with stars, but one exchange towered over all the others in his 50-year career.

"You've explained how you have got caught up in this thing," he told Richard Nixon in his famous 1977 TV interviews with the disgraced former president. "You've explained your motives: I don't want to quibble about any of that. But just coming to the substance: Would you go further than 'mistakes' — the word that seems not enough for people?"

Nixon — three years after stepping down from office in the wake of Watergate — astonished the unflappably British Frost by appearing to acknowledge that "mistakes" may have been too mild a term.

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"What word would you suggest?" Nixon asked.

In a 2007 interview with Timothy Naftali, then director of the Richard Nixon Presidential Library & Museum, Frost called it "the most heart-stopping answer I've ever heard."

"I knew that he was more vulnerable at that moment than he probably ever would be again and that I must phrase my response in order to get that across," Frost said. "And I threw down my clipboard to indicate that this was not a scripted job, that this was not a prepared ambush…."

An interviewer who proved as adept at probing the inner Nixon as he was at asking celebrities their secrets to a successful marriage, Frost died Saturday night, apparently of a heart attack, while aboard the cruise liner Queen Elizabeth, his family said. He was 74.

He was scheduled to give a shipboard speech and died en route from England to Portugal.

Frost interviewed the last eight British prime ministers and the seven U.S. presidents who held office from 1969 to 2008, according to the Associated Press. His Nixon interviews were the most widely watched news programs broadcast anywhere until that time.

"He could be — and certainly was with me — both a friend and a fearsome interviewer," British Prime Minister David Cameron said in a statement Sunday.

Dick Cavett told the L.A.Times on Sunday that he admired Frost for "his fits of incisiveness."

"He was excessively polite at times," veteran interviewer Cavett said, "and then he would burst out of that and just skewer somebody with a short dagger."

When Frost interviewed U.S. Rep. Adam Clayton Powell Jr. of New York, he wouldn't let the politician off the hook for his alleged misuse of public funds.

"Being his elegant, arrogant, contemptuous self, Powell used the phrase, 'I've paid my dues' at least three times," Cavett said. "On the fourth time, David said: 'We've all heard enough of your wretched dues!' I wanted to kiss him for that and so did everyone in the studio audience."

Frost's best-known interview was with Nixon and it was controversial well before it was aired. Even though the former president was to break his silence for the first time since leaving office, the three major networks wouldn't run Frost's four 90-minute programs. By paying Nixon $600,000, Frost had breached CBS' ethical code, the network ruled. ABC and NBC declined because their own personnel had not been involved.

But Frost, taping more than 28 hours with Nixon at a Dana Point home, contracted with individual stations and made global headlines. Under his questioning, Nixon, at times combative and at others almost teary, acknowledged Watergate's toll.

"I let down my friends," he told Frost. "I let down the country. I let down our system of government and the dreams of all those young people that ought to get into government but think it's too corrupt.... I let the American people down, and I have to carry that burden with me the rest of my life."

Nixon denied committing any crimes or impeachable offenses but said he had lied to the American people while under fierce attack from a "fifth column" of political enemies and journalists.

"I brought myself down," he told Frost, a TV host long known to Americans. "I gave 'em a sword and they stuck it in, and they twisted it with relish. And I guess if I'd been in their position, I'd have done the same thing."

In response to Nixon's question about a better word than "mistake," Frost suggested the ex-president acknowledge wrongdoing in the White House and apologize for "putting the American people through two years of needless agony." In his rambling, 20-minute reply, an emotional Nixon said he'd let America down.

The sessions between Frost and Nixon were dramatized in "Frost/Nixon", a 2006 Peter Morgan play and a 2008 movie starring Michael Sheen as Frost and Frank Langella as Nixon

Born April 7, 1939, in Tenterden, England, David Paradine Frost, the son of a Methodist minister, attended Cambridge. Active in the Cambridge Footlights, a theatrical group, he was later discovered in a nightclub by a BBC director who was impressed by his impersonation of Prime Minister Harold Macmillan.

In 1962, Frost became host of "That Was the Week That Was," a new BBC satirical revue. The following year, he started the same program in the U.S., setting the table for the hard-edged topical comedy of later shows like "The Smothers Brothers Comedy Hour" and "Saturday Night Live. "

He was relentlessly ambitious and could be arrogant, though his staff seemed to take it with a smile. According to Times columnist Joyce Haber, Frost's secretary is said to have circulated a verse she wrote about him: "A general once lived named DeGaulle/500 years old,10 feet tall/he thought he was God/which really was odd/for God's David Frost, if at all."

Successful both in the U.S. and in Britain, Frost jetted between the two for decades, interviewing celebrities as varied as Timothy Leary and Tex Ritter, Billy Graham and Raquel Welch.

He also hosted "Through the Keyhole," visiting homes of the rich and famous in Britain.

Critics liked him — The Times called him "rare beefsteak in a marshmallow sundae world" — but some were put off by his hunched-over posture and studied intensity. Writer Peter Heller likened him to "a bemused and somewhat undernourished bird of prey transfixed by a being it finds too fascinating to attack."

Frost, who was knighted in 1993, married Lady Carina Fitzalan-Howard, daughter of the Duke of Norfolk, in 1983. She survives him as do their three sons.

At the time of his death, Frost hosted an interview show for Al Jazeera English.

Talking with the Sunday Telegraph in London last year, he chuckled when asked about critics' occasional complaints that he had "gone soft."

He said former Labour Party leader John Smith once told him: "David you have a way of asking beguiling questions with potentially lethal consequences."

"I'd be happy to have that on my tombstone," Frost said.

steve.chawkins@latimes.com

Times staff writer Elaine Woo contributed to this report.