MOUNT VERNON, VIRGINIA (NYTIMES) - Mr G. Gordon Liddy, a cloak-and-dagger lawyer who masterminded dirty tricks for the White House and concocted the bungled burglary that led to the Watergate scandal and the resignation of President Richard Nixon in 1974, died on Tuesday (March 30) in Mount Vernon, Virginia. He was 90.

His death, at the home of his daughter Alexandra Liddy Bourne, was confirmed by his son Thomas P. Liddy, who said that his father had Parkinson's disease and had been in declining health.

Decades after Watergate entered the lexicon, Mr Liddy was still an enigma in the cast of characters who fell from grace along with the 37th president. To some, he was a patriot who went silently to prison refusing to betray his comrades; to others, a zealot who cashed in on bogus celebrity to become an author and syndicated talk show host.

As a leader of a White House "plumbers" unit set up to plug information leaks, and then as a strategist for the president's re-election campaign, Mr Liddy helped devise plots to discredit Nixon's "enemies" and to disrupt the 1972 Democratic National Convention. Most were far-fetched - bizarre kidnappings, acts of sabotage, traps using prostitutes, even an assassination - and were never carried out.

But Mr Liddy, a former Federal Bureau of Investigation (FBI) agent, and Mr Howard Hunt, a former agent with the Central Intelligence Agency, engineered two break-ins at the Democratic National Committee offices in the Watergate complex in Washington. On May 28, 1972, as Mr Liddy and Mr Hunt stood by, six Cuban expatriates and Mr James McCord, a Nixon campaign security official, went in, planted bugs, photographed documents and got away cleanly.

A few weeks later, on June 17, four Cubans and Mr McCord, wearing surgical gloves and carrying walkie-talkies, returned to the scene and were caught by the police. Mr Liddy and Mr Hunt, running the operation from a Watergate hotel room, fled but were soon arrested and indicted on charges of burglary, wiretapping and conspiracy.

In the context of 1972, with Nixon's triumphal visit to China and a steamrolling presidential campaign that soon crushed the Democrat Senator George McGovern, the Watergate case looked inconsequential at first. Nixon's press secretary, Mr Ron Ziegler, dismissed it as a "third-rate burglary".

But it deepened a White House cover-up that had begun in 1971, when Mr Liddy and Mr Hunt broke into the office of the psychiatrist of military analyst Daniel Ellsberg - who had leaked the Pentagon Papers to The New York Times - looking for damaging information on him. Over the next two years, the cover-up unravelled under pressure of investigations, trials, hearings and headlines into the worst political scandal - and the first resignation by a sitting president - in the nation's history.

Unlike the other Watergate defendants, Mr Liddy refused to testify about his activities for the White House or the Committee to Re-elect the President, and drew the longest term among those who went to prison. He was sentenced by Judge John J. Sirica to six to 20 years, but served only 52 months. President Jimmy Carter commuted his term in 1977.

"I have lived as I believed I ought to have lived," Mr Liddy, a small, dapper man with a baldish pate and a brushy moustache, told reporters after his release. He said he had no regrets and would do it again.

"When the prince approaches his lieutenant, the proper response of the lieutenant to the prince is, 'Fiat voluntas tua'," he said, using the Latin of the Lord's Prayer for "Thy will be done".

Disbarred from law practice and in debt for US$300,000 (S$403,000), mostly for legal fees, Mr Liddy began a new career as a writer. His first book, Out Of Control (1979), was a spy thriller. He later wrote another novel, The Monkey Handlers (1990), and a non-fiction book, When I Was A Kid, This Was A Free Country (2002). He also co-wrote a guide to fighting terrorism, Fight Back! Tackling Terrorism, Liddy Style (2006), and produced many articles on politics, taxes, health and other matters.

In 1980, he broke his silence on Watergate with his autobiography, Will. The reviews were mixed, but it became a bestseller. After years of revelations by other Watergate conspirators, there was little new in it about the scandal, but critics said his account of prison life was graphic. A television movie based on the book was aired in 1982 by NBC.

Mr Liddy found himself in demand on the college-lecture circuit. In 1982, he teamed up with Mr Timothy Leary, the 1960s LSD guru, for campus debates that were edited into a documentary film, Return Engagement.

The title referred to an encounter in 1966, when Mr Liddy, as a prosecutor in Dutchess County, New York, joined a raid on a drug cult in which Mr Leary was arrested.

In the 1980s, Mr Liddy dabbled in acting, appearing on Miami Vice and in other television and film roles. But he was better known later as a syndicated talk-radio host with a right-wing agenda.

The G. Gordon Liddy Show, which began in 1992, was carried on hundreds of stations by Viacom and, later, Radio America, with satellite hook-ups and Internet streaming. It ran until his retirement in 2012. He lived in Fort Washington, Maryland.

Mr Liddy, who promoted nutritional supplements and exercised, was still trim in his 70s. He made parachute jumps, took motorcycle trips, collected guns, played a piano and sang lieder. His website showed him craggy-faced with head held high, an American flag and the Capitol dome in the background.

He was born George Gordon Battle Liddy on Nov 30, 1930, in Brooklyn to Mr Sylvester J. Liddy and Mrs Maria Liddy. He grew up in Hoboken, New Jersey, a fearful boy with respiratory problems who learnt to steel himself with tests of willpower.

He lifted weights, ran and, as he recalled, held his hand over a flame as an act of self-discipline. He said he once ate a rat to overcome a repulsion, and decapitated chickens for a neighbour until he could kill like a soldier, "efficiently and without emotion or thought".

Like his father, a lawyer, Mr Liddy attended the all-male St Benedict's Prep School in Newark and Fordham University in the Bronx. After graduating from Fordham in 1952, he took an army commission with hopes of fighting in South Korea, but was assigned to an anti-aircraft radar unit in Brooklyn. In 1954, he returned to Fordham and earned a law degree three years later.

In 1957, he married Ms Frances Ann Purcell. The couple had five children. Along with his son Thomas and daughter Alexandra, he is survived by another daughter, Ms Grace Liddy; two other sons, Mr James Liddy and Mr Raymond J. Liddy; a sister, Ms Margaret McDermott; 12 grandchildren and two great-grandchildren. Mr Liddy's wife died in 2010.

From 1957 to 1962, Mr Liddy was an FBI field agent in Indianapolis and Gary, Indiana, as well as Denver, Colorado, and a supervisor of crime records in Washington. He then worked in patent law for his father's firm in New York for four years. He joined the Dutchess County district attorney's office as an assistant prosecutor in 1966.

In 1968, he began a dizzying, three-year rise from obscurity in Poughkeepsie, New York, to the White House. Challenging Mr Hamilton Fish Jr in a primary for the Republican nomination for Congress in what was then New York's 28th District, he fell short, but his consolation prize was to take charge of the Nixon campaign in the mid-Hudson Valley, which the president won handily.

His reward was a job at the Treasury Department in Washington as a special assistant for narcotics and gun control. He helped develop the sky marshall programme to counteract hijackers. Impressed, Mr Egil Krogh, a deputy assistant to the president, recommended him in 1971 to Mr John Mitchell, the attorney-general, who recommended him to Mr John Ehrlichman, the president's domestic policy adviser.

Nixon, furious over the disclosure of the Pentagon Papers, had directed Mr Ehrlichman to set up the "plumbers" to plug leaks and punish opponents. Among other operations, Mr Liddy and Mr Hunt, who were in charge of the unit, broke into the Beverly Hills, California, office of Mr Ellsberg's psychiatrist, Mr Lewis Fielding, for material to discredit the military analyst. They found none.

When the group was disbanded in 1971, Mr Liddy went to work for the Nixon campaign. His title was general counsel, but his role was to plot more dirty tricks under a code name, "Gemstone".

They included kidnapping radicals who might disrupt the Republican convention, sabotaging the air-conditioning at the Democratic convention in Miami, hiring prostitutes to entrap Democrats with hidden cameras, and killing syndicated columnist Jack Anderson, whom Mr Liddy viewed as a national security risk.

But only the Watergate burglaries were carried out. It was a piece of tape over the lock on a garage-level door that tripped up the burglars. A security guard called the police, and a crackling walkie-talkie in Mr Liddy's hotel room told the tale: "It looks like… guns!" one burglar whispered. "They've got guns. It's trouble."

The team's lookout, in an apartment across the street, broke in: "Now I can see our people. They've got their hands up. Must be the cops. More cops now. Uniforms… "

"They got us!" It was all over. Mr Liddy and Mr Hunt went home. It was 3am when Mr Liddy got in, and his wife awoke. "Anything wrong?" she asked.

"There was trouble," he said. "Some people got caught. I'll probably be going to jail."