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Cambridge, England • Margaret Thatcher felt betrayed by close ally President Ronald Reagan over the Falkland Islands, according to newly released papers that reveal how isolated Britain's prime minister was in her determination to repel the Argentine invasion by force.

When Argentina seized the British territory off the South American coast in April 1982, Thatcher's government presented a united front in public.

But private papers released Friday by the Thatcher archive at Cambridge University show that the British leader's closest advisers urged her to negotiate over the islands' future rather than go to war. And the Reagan administration backed a peace plan that called for Britain to drop its insistence on self-determination for the islanders — a stance that led Thatcher to say Anglo-American friendship had brought her "into conflict with fundamental democratic principles."

The war was one of the pivotal moments of Thatcher's career. But many doubted she would triumph in retaking the South Atlantic islands, 8,000 miles (13,000 kilometers) from London and home at the time to fewer than 2,000 people.

On April 6, four days after the invasion, Chief Whip Michael Jopling sent Thatcher a note outlining the views of Conservative lawmakers.

The blunt assessments ranged from "my constituents want blood ... invade as quickly as possible" to "we are making a big mistake." One lawmaker was described as "hopelessly defeatist, depressed and disloyal," another as "desperately depressed."

Historian Chris Collins of the Margaret Thatcher Foundation said the documents reveal confusion, uncertainty and dismay inside 10 Downing St.

"I think the range of opinion and the degree of confusion is startling," Collins said. "Particularly in the first few weeks, people don't know how to react."

Thatcher's opponents weren't just the liberal "wets" she often derided, but loyal lieutenants who shared her uncompromising economic policies.

Thatcher's economic adviser, Alan Walters, wrote in his diary — also made public Friday — that he had proposed that "we should get Argentina to pay compensation to the Falklanders."

John Hoskyns, head of Thatcher's policy unit, wrote in his diary of his fear "that we are about to make almighty fools of ourselves."

He said it would be sad if the Falklands "precipitated the downfall of the Thatcher government and the long-run effect was that the country ended up with an economy unable to sustain proper defense for 56 million people rather than 1,800."

Meanwhile, former Thatcher adviser Alfred Sherman confided to Hoskyns that the Foreign Office, which had urged restraint, "is staking everything on a defeat for Margaret, to prove themselves right all along."

Thatcher was especially stung by Reagan's stance. A Peruvian peace plan backed by the United States called for a cease fire but insisted the U.K. give up its insistence on the Falklands remaining British.

Thatcher's War Cabinet agreed — but it's clear from the papers that the prime minister remained opposed to the concession.

Her hurt and anger shine through a hand-written letter to Reagan, her strongest international ally.

"I think you are the only person who will understand the significance of what I am trying to say," Thatcher wrote on May 5.

"That our traditional friendship, to which I still loyally adhere, should have brought me and those I represent into conflict with fundamental democratic principles sounds impossible while you are at the White House and I am at No.10.

"I too want a peaceful settlement but we really must put up a more formidable diplomatic fight for the Falklanders and for others who may be similarly treated if we fail."

Collins said Thatcher felt betrayed and "profoundly let down" by Reagan.

The letter Thatcher drafted was never sent. A toned-down version was posted, but by then Argentina had rejected the peace plan.

Britain retook the islands on June 14 after a battle that killed 649 Argentines, 255 British troops and three islanders.

Thatcher's popularity surged after the victory, and her government easily won reelection in 1983. She led the country until 1990, transforming Britain's economy with her free-market policies.

The files contain letters hailing Thatcher's Falklands victory — some from unlikely sources. The leftist Revolutionary Democratic Front of El Salvador sent flowers and a note of thanks, saying Thatcher had "succeeded where we failed" and got Argentina to withdraw military advisers from Central America.

Among her more surprising fans was spy novelist John le Carre, who expressed regret as he turned down an invitation to a literary dinner party attended by Thatcher.

"Please give her my good wishes if you have a chance," le Carre, a critic of successive British governments, wrote to dinner host Hugh Thomas. "I never thought I could find her admirable, but I do somehow. Perhaps because I do believe she is an honest and extraordinarily brave person."