A group of American oil executives whose firms have employes in Libya were invited to the State Department yesterday and advised to begin an "orderly drawdown" of their personnel.

State Department sources said after the closed-door meeting that they did not suggest a fast, mass evacuation nor was their warning based on anything specific that the United States anticipates happening to the 2,000 or so Americans who work for roughly 50 U.S. firms, mostly energy companies.

Rather, officials said they called the company executives to the department to make sure they fully understood the possibilities of some unanticipated problems and to say that the U.S. government was not in a position to protect and assist them if trouble comes.

The unusual, hour-long meeting was attended by more than 30 company officials. It came in the aftermath of the Reagan administration decision, announced Wednesday, to expel all Libyan diplomats in this country (except those at the United Nations) for "provocations and misconduct, including support for international terrorism" and what White House officials yesterday described as "a continuing pattern of threatening, harassing and intimidating residents of this country" who are foes of the controversial Libyan leader, Col. Muammar Qaddafi.

Though the State Department has declined to make public specific details behind the ouster, numerous diplomatic and law enforcement officials claim privately that there is ample evidence of Libyan government efforts to silence Qaddafi's critics here and in Europe, where eight dissidents were murdered last year.

The top Libyan diplomat here, Ali Houderi, said in television interviews yesterday that the Americans in Libya were safe there. He said he did not anticipate any cutoff of U.S. oil sales by Libya, though he said anything was possible now and everybody would have to wait and see the reaction of this country. "Nobody else can dictate to us," he said.

Houderi, along with 26 other diplomats and their families, were packing their bags yesterday; they have until midnight Wednesday to be out of the country.

Libya is the third largest foreign supplier of U.S. oil, a business that yields Libya about $12 billion a year and satisfies about 10 percent of U.S. import needs. The two-way benefits of this trade have survived deep shocks in the past. When Libya broke relations completely with Washington for a while in 1967 over the Arab-Israeli war, the Tripoli regime continued to sell oil.

Now the two countries are just one step short of another formal break in relations. Initial reports from a few officials whose firms were at yesterday's meeting indicated that companies were adopting a wait-and-see attitude. There was no immediate indication that companies would begin pulling out U.S. citizens or that the diplomatic quarrel would spill over into the lucrative business connections.

The White House and State Department have also said they saw no reason why the expulsion order should affect the oil relationship. Yesterday, however, officials were unable to say how that relationship would be affected if U.S. firms followed the government's advice and withdrew their employes.

State Department sources said the meeting yesterday was useful both for the companies and the government. The department learned exactly which companies were in Libya and who their employees were. Presumably this information would be vital if there were some emergency there.