A chartered jetliner airlifted most of Mobil Oil's American employes out of Libya today in compliance with orders from Washington that have caused anguish among U.S. residents here and clouded the future of U.S. companies cashing in on Libya's oil wealth.

The U.S.-bound Lufthansa plane lifted into a feeble winter sun with 68 evacuees, in response to the pullout of U.S. citizens ordered by President Reagan after the United States accused Libya of plotting to assassinate U.S. officials.

But the complaints of those remaining behind -- for the time being -- illustrated the extent to which U.S. businessmen and their dependents here judge the administration's action unwise.

A crucial moment for the future of U.S. companies here had been set for next week, when negotiations were to begin on 1982 contracts between the companies and Libya's National Oil Co. Ordinarily, top executives of the six U.S. oil firms still operating here would fly to Tripoli for the talks. Now, however, Reagan has in principle barred travel here by U.S. citizens.

The key lies in talks between oil companies and the State Department on whether the companies will be authorized to continue operations here and, if so, whether Libya-based executives will be allowed to stay on to arrange for an orderly transition to European personnel, oil officials said. Talks with a number of Americans indicated few, if any, will try to remain in Libya in defiance of U.S. orders.

Whatever the economic losses, U.S. executives here characterize the administration's confrontation with Libyan leader Muammar Qaddafi as bewildering. Cecil Kersting, a Mobil geologist, said he had not heard of any anti-American incidents such as rock throwings, which he said would be signs of the danger cited by Washington.

At the same time, observers recalled that the U.S. Embassy here was sacked in December 1979 by a mob unhindered by Libyan police. Although U.S.-Libyan diplomatic relations were not severed formally, U.S. diplomats were recalled and Libyan diplomats have since been expelled from the United States on charges that they were connected with attacks on dissident Libyans.

Voicing the view of many U.S. residents, Ruth Monson, whose husband runs the Oil Field Companies School here, said, "The Libyans aren't vicious people. Of course, there are good and bad in every country," she added. "Our question is, where does the danger lie? Does it lie from the Libyans, or from the Reagan administration?"

Her remarks reflected the disruption in the lives of 1,500 Americans living here, most of whom are connected with the oil industry or related companies, because of the administration moves -- as well as their disbelief of its contention that Americans are in "imminent danger" from the Qaddafi government.

Oil executives and European diplomats here also questioned whether the U.S. gesture in the long run will have any effect on the Libyan oil industry, except to complicate operations for American companies. Privately, the diplomats and oil men unanimously predicted that, if permission is given, the U.S. companies will replace Americans with Europeans and keep on pumping.

European diplomatic sources said the U.S.-Libyan showdown came at a particularly inopportune time for the American oil firms. Since the summer, Libyan oil prices have been so high that production has declined drastically. But authorities this month began offering "discounts" that, in effect, lowered the price per barrel from $37.50 to as low as $35.25 for "equity oil" marketed by the companies themselves, the sources said.

As a result, production has climbed steadily since Dec. 1, reaching more than 1 million barrels a day after a low of 700,000 last month, they added. Although the new level is still below the more than 1.7 million barrels a day of a year ago, it gives Qaddafi's treasury a much-needed infusion, they said.

"They have been getting reduced revenues for the last six months, and it's beginning to bite," said one diplomatic observer.

The Libyan leader keeps such figures a secret, but Qaddafi's intervention in neighboring Chad is estimated here to have cost about $2 billion. In previous years, this would amount to relatively little. Following the fall production slump, however, the Chad operation is believed to have been a factor in Libyan belt-tightening.

U.S. charges that Qaddafi has dispatched hit teams to assassinate Reagan or his top aides -- the immediate cause of Washington's recent action -- were met with denials by Qaddafi and his followers and with caution by European diplomats posted here.

The Europeans, reflecting their governments' attitudes, expressed reserve about the public confrontation launched by the U.S. administration, particularly on the basis of proof of which, the diplomats said, they have not been informed. But, against a background of terror strikes in European capitals attributed to Libyan agents, they did not dismiss the U.S. accusations.