Two American military officers and two European officers attached to the U.N. observer force were killed yesterday in Lebanon when their Jeep struck a land mine east of Beirut, U.S. government officials said.

The Pentagon identified the officers as Army Maj. Randall A. Carlson, 35, of Derwood, Md., and Air Force Maj. Harley S. Warren, 34, of Valdese, N.C. They were not part of the 3,000-member multinational peace-keeping force of U.S. Marines and Italian and French troops waiting to land in Beirut.

President Reagan expressed his "deep regret" at the deaths, which occurred at 1 p.m. EDT yesterday.

Those killed in the explosion nine miles east of Beirut did not have "any connection with the multinational force," Reagan said.

Meanwhile, the State Department expressed optimism last night that snags holding up the deployment of the multinational force in West Beirut had been resolved, and administration sources said that the troops are expected to be in position by Tuesday or Wednesday.

"There is substantial progress following talks which Ambassadors Philip Habib and Morris Draper had today with Israel," State Department spokesman Rush Taylor said yesterday.

The deaths of the two American officers were announced by the U.S. government.

"Two U.S. officers assigned to the U.N. observer force in Lebanon and on temporary duty with the special observer team in Beirut were killed today at 1 p.m. EDT when the Jeep in which they were riding struck a mine in the vicinity of the Beirut-Damascus highway approximately 15 kilometers about 9 miles east of Beirut," a Defense Department spokesman said.

"We understand that an Irish major and a Finnish captain were also in the Jeep and were also killed," the spokesman said.

Senate Majority Leader Howard H. Baker Jr. (R-Tenn.) said the deaths heightened his concern about the reintroduction of U.S. Marines into the area, but he continues to support Reagan's decision to do so.

Administration officials at the White House, Pentagon and State Department were quick to point out that the incident occurred some distance from Beirut, in an area where the multinational force is not expected to be deployed.

The speed with which officials put some distance between the U.N. operations and the multinational force reflected the continuing sensitivity about putting U.S. troops into a potentially dangerous situation.

Senior military officials are known to be concerned about the possible exposure of U.S. forces in the violent climate of Lebanon, and this concern is believed to be one of the reasons for the quick exit of the first multinational force, which was sent to supervise the departure of Palestine Liberation Organization forces from the Israeli-encircled Lebanese capital.

The United Nations maintains a 7,000-man force in southern Lebanon as a buffer between Israeli and Palestinian forces.

Israel maintained that this buffer unit was largely ineffective, and launched its drive into southern Lebanon in June to drive out PLO guerrilla forces in the region.

In addition to the forces in southern Lebanon, the United Nations maintains a small observer force in Beirut. The dead Americans were attached to this force, although it was unclear what they were doing miles east of the capital when their Jeep hit the land mine yesterday.

Both Lebanon and Israel objected to a U.N. force being sent to West Beirut after the massacre of Palestinians there last week, and this prompted the reconstituting of the joint U.S.-French-Italian force.

Some 350 French troops landed in Beirut Friday, but have refused to move out from their positions in the French Embassy compound until Israel pulls its forces out of the predominantly western part of the Lebanese capital.

Reagan had demanded that Israel pull its troops out of Beirut as the first stage of a withdrawal from Lebanon and as part of the arrangement to get the multinational force deployed.

According to reports from the Lebanese capital, Italian officials had joined the French in refusing to deploy their troops until the Israelis were out of the way.