Libya has pledged to assume responsibility for the 1988 bombing of Pan Am Flight 103 over Lockerbie, Scotland, and to pay $2.7 billion in compensation to relatives of the 270 victims in exchange for a formal end to an 11-year United Nations embargo, U.N. diplomats said today.

U.S., British and Libyan officials completed the terms of the agreement at a meeting in London on Monday, concluding more than four years of negotiations. If Libya follows through, it would be the first time that the government of Libyan leader Moammar Gaddafi has admitted any involvement in the jet bombing that killed all 259 people aboard and 11 on the ground.

Diplomats familiar with the discussions cautioned that the deal could still unravel if Libya reneges on its commitment. But one U.N.-based diplomat who has been briefed on the talks said the "shape" of the pact has been "agreed to" in London.

According to a tightly choreographed schedule worked out at the London talks and in discussions with lawyers representing the victims' relatives, Libya is expected to sign an agreement Wednesday with the relatives' lawyers in Basel, Switzerland. The Libyans would then begin depositing $2.7 billion into an escrow account at the Bank for International Settlements in Switzerland.

The Libyan government on Thursday is scheduled to present the president of the U.N. Security Council a letter acknowledging for the first time that Abdel Basset Ali Megrahi, who was convicted by a Scottish court in the Netherlands in 2001 for his role in the bombing, was indeed a Libyan agent, said U.N. diplomats familiar with the negotiations. The court acquitted a second Libyan suspect. However, the letter would not hold Gaddafi and his government directly responsible for ordering the attack, the officials said.

If the terms are met by Libya, the United States and Britain will present to the Security Council president on the same day a letter indicating that Libya had complied with the demands of the U.N. sanctions resolution. Britain would then introduce a Security Council resolution as early as Friday calling for the formal lifting of the sanctions.

A vote could take place next week. The United States is considering abstaining, according to a U.N. diplomat.

State Department spokesman Philip T. Reeker said "we're pleased with the progress that's been made" in the London talks, but he stopped short of confirming that a final deal had been struck.

The Security Council suspended the sanctions in 1999 after Libya turned over the two Libyan suspects for trial. But the United States has maintained a separate embargo, saying that the Libyan government remains a state sponsor of terrorism.

The Security Council imposed an air, arms and partial oil equipment embargo on Libya in 1992 and 1993 to compel Gaddafi's government to surrender the Libyan suspects for trial. To have the sanctions lifted permanently, Libya must pay compensation to the families of the victims, take responsibility for the attack, renounce terrorism and agree to cooperate on the settlement terms.

In a possible hitch in the latest agreement, France has indicated that it wants to delay a council vote to allow lawyers to strike a better deal for the families of the victims of the September 1989 bombing of a French UTA jet. That blast killed 170 passengers and crew members as they flew over Niger. A French court ruled that Libyan agents bombed the aircraft. The victims' families received between $3,000 and $30,000 each.

"We have always shown solidarity with our partners throughout this painful affair," the French Foreign Ministry said in an Aug. 8 statement. "We expect that they would also show solidarity towards the victims of UTA Flight 772."

Lawyers representing the families of the victims of the Pan Am 103 bombing struck a deal with Libyan officials last year involving a $10 million payment to each victim's family. An initial $4 million would be paid once U.N. sanctions have been formally lifted. An additional $4 million would be paid once the United States lifts its sanctions. The final $2 million would be delivered if Libya is removed from the State Department's list of states allegedly sponsoring terrorism.

William Burns, the U.S. assistant secretary of state for Near Eastern and North African affairs, is planning a Friday meeting in Washington for the relatives of the victims of the Pan Am bombing, according to U.N. diplomats and some relatives.

The 1988 terrorist bombing of Pan Am Flight 103 over Lockerbie, Scotland, killed 270 people.