WASHINGTON – Former FBI Deputy Director W. Mark Felt was unmasked yesterday as Deep Throat, www.xxxdeepthroat.com, the shadowy government official who helped The Washington Post unravel the coverup that forced President Richard Nixon’s resignation.

Finally lifting a 30-year veil on the greatest political and journalistic mystery of modern-day Washington, the Watergate reporting duo of Bob Woodward and Carl Bernstein confirmed Felt’s identity on The Post’s Web site hours after a Vanity Fair article first broke the story.

Earlier, Woodward and Bernstein issued separate statements reiterating their longstanding intention to reveal their most famous source’s identity only after his death.

But after the Vanity Fair article and a subsequent statement from Felt’s family confirming his identity, Woodward and Bernstein decided to go public.

Former Post executive editor Ben Bradlee, who ran the paper during the Watergate scandal, told The Post he knew at the time that Deep Throat was a senior FBI official and learned his name shortly after Nixon’s resignation on Aug. 9, 1974.

“The thing that stuns me is that the goddamn secret has lasted this long,” Bradlee added. “I’ve never met Felt. I wouldn’t know him if I fell on him.”

Now 91 and living with his daughter in Santa Rosa, Calif., Felt suffered a stroke in 2001 and is in declining health. In a poignant made-for-TV moment, he appeared at the door of her home, smiling broadly and clinging to his walker as he posed for photographs.

“He’s grinning from ear to ear,” daughter Joan Felt said. “He’s always lived with honor. He’s a great patriot.”

In the Vanity Fair blockbuster, John O’Connor wrote that “On several occasions [Felt] confided to me: ‘I’m the guy they used to call Deep Throat.'”

A lawyer and former federal prosecutor, O’Connor says Felt kept the secret from his family until 2002, when a close friend told his daughter that Felt had divulged his secret in the 1980s.

According to the account, Joan Felt confronted him: “I know now that you’re Deep Throat.” He replied, “Since that’s the case, well yes, I am.”

Felt – who has always vigorously dismissed speculation that he was the supersource – has figured prominently in speculation about Deep Throat’s identity for decades because he was one of a handful of officials with access to FBI files involving the break-in. Watergate aficionados have always believed only someone with knowledge of what Nixon political aides were telling FBI agents could have been The Post’s source.

The Vanity Fair story suggests that Felt, whose complicity in the Woodward-Bernstein leaks was suspected at the time by top Nixon aides, was troubled by White House and Justice Department attempts to “stonewall” the truth and impede the FBI’s investigation.

“Felt came to see himself … as something of a conscience of the FBI,” the article noted.

It also makes clear that Felt’s children and grandchildren have pressed the old man to disclose his involvement so he could be honored for his patriotism during his lifetime.

Obsessed with protecting his identity, Deep Throat met with Woodward in secluded places like underground parking garages, giving him information and advice that helped keep Woodward and Bernstein on the trail of the coverup ordered by Nixon and his top lieutenants to conceal their knowledge of the break-in at Democratic National Committee headquarters on June 17, 1972.

“I’m greatly surprised and shocked that it’s him,” Cartha (Deke) DeLoach, a key lieutenant of FBI Director J. Edgar Hoover, told the Daily News.

“He was a very strict, strait-laced individual who was very quiet and he never spoke to the press at all, to my knowledge, when I knew him,” DeLoach said. Leaking to The Post “would be totally out of his character.”

Watergate revisited

Watergate, the botched burglary that brought down a President, is a dimming memory to Americans, many of whom weren’t born or were just kids when the scandal rocked the nation. Here’s a little refresher:

What was Watergate?

An act of political espionage committed on the night of June 17, 1972, when five burglars broke into the Democratic National Committee offices in the Watergate office complex in Washington.

What did President Nixon do?

He tried to cover up White House involvement in the burglary and a campaign of “dirty tricks” against Democratic rivals. He insisted “no one on the White House staff, no one in this administration … was involved” in Watergate.

Nixon tried to keep Oval Office audiotapes from special prosecutor Leon Jaworski because they would prove Nixon was personally involved in the payment of hush money to the burglars.

Who was Deep Throat?

A secretive source for Washington Post reporters Bob Woodward and Carl Bernstein who guided them through their investigation with Yoda-like advice like, “Follow the money.”

What were the consequences?

Facing the prospect of an impeachment vote in the House, Nixon became the first U.S. President to resign.