Warnings about another terrorist attack against Americans in Beirut before the Nov. 6 U.S. presidential election have heightened tensions among U.S. officials here, prompting them to restrict tightly their movements around the capital and to curtail most face-to-face contact with nonembassy personnel.

The security precautions have compounded the physical difficulty confronting officials trying, from often widely scattered locations, to carry on diplomatic functions after a car bomb that severely damaged the U.S. Embassy annex in east Beirut on Sept. 20.

Underscoring the new tensions was a decision to have the few dependents of diplomatic personnel in the country leave. The announcement, made today by the State Department in Washington, said five or six dependents were evacuated to an undisclosed location.

Only a few dependents of embassy personnel had returned here after all family members had been evacuated last February following the takeover of west Beirut security by Moslem militia. Rose-Anne Bartholomew, wife of Ambassador Reginald Bartholomew, is said still to be in the country.

No decision has been made yet on whether to reconstruct the partially destroyed annex in the Christian suburb of Aukar or to move personnel into a newly readied embassy facility in west Beirut, according to well-informed sources.

The new precautions by American personnel come amid fresh intelligence reports that not all of the explosives brought into the country for the Aukar attack were used at that time and that another attack, possibly on the same facility, is anticipated before the American presidential election on Nov. 6.

Most of the U.S. Embassy staff shifted in August from living and working in the Moslem-dominated western sector of the city to new quarters and offices in east Beirut, believing that the Christian half of the capital was safer.

All relocation decisions are understood to be on hold until after the November election. The embassy staff has adopted what one member terms a "wait-and-see mode."

Officials here, sensitive to the repercussions that anything said might have on the political debate about Lebanon in the presidential campaign, are very reluctant to discuss their situation.

Meanwhile, a senior Lebanese government official expressed concern today about the possibility of the Reagan administration eventually closing the U.S. Embassy in Beirut. The official, who spoke on the condition that he not be named, said that an embassy pullout would be regarded far more seriously than the withdrawal in February of the U.S. Marine contingent.

"We can understand the low profile that the administration wants to take now for reasons of party politics," said the official. "But if this were to continue after the election, it would be a reversal of all we have heard about the United States not bowing to terrorism. It would seriously undermine the credibility of the American government."

The embassy staff is down to about 40 persons, half of whom are support personnel, including a small contingent of U.S. Marine guards. Another 30 military officers are stationed in east Beirut as part of a continuing U.S. training program for the Lebanese Army.

During the day, embassy functions are scattered around the eastern part of Beirut.

Ambassador Bartholomew and two aides operate out of the ambassador's residence in the suburb of Baabda, several miles east of the city's center and next to the presidential palace.

Some administrative personnel have returned to work at the annex in offices that escaped destruction. Other employes are said by U.S. sources to be working out of their apartments.

At night, the diplomats and military personnel are housed in a number of apartment blocks situated at various Christian neighborhoods in the hillside suburbs of east Beirut.

All U.S. consular services have been shut down since the bombing. Foreign travelers seeking a visa to the United States are being directed to U.S. embassies in Cyprus or Damascus.

Many of the contacts U.S. officials now have with local political, business and media people are limited to phone calls. West Beirut has been placed off-limits to the diplomats and military trainers, and evening socializing in public places in east Beirut has been discouraged.

Even occasional luncheon appointments in public restaurants are made with close attention to security.

One official, agreeing to meet a friend for lunch outside embassy offices, suggested one restaurant on the phone and then, in person and at the last minute, switched the meeting to another restaurant, citing security concerns.

To thwart feared kidnaping or assassination attempts against individual embassy staff members, U.S. officials are also varying their daily travel schedules and other activities. Current security restrictions on U.S. personnel here are said to be stricter than those that applied in the first half of the year, when the diplomats were virtually holed up in a heavily guarded seaside compound in west Beirut.

American correspondents in Beirut received renewed and more emphatic warnings from U.S. officials this week of possible kidnaping or other attacks against American citizens living here who are less protected than the diplomats and military trainers. One official observed that as the more intensified security precautions are instituted for embassy personnel, other U.S. targets become more likely prospects for attack by terrorists operating in Beirut.

A number of western embassies, in addition to the American, have tightened security in response to an assortment of threats also made against them. But one European diplomat sounded a note of concern about the American nervousness, suggesting that it might be impeding calm analysis of the many threats received.