The five U.S. oil companies with holdings in Libya said yesterday that they have not been told of a possible Reagan administration order to cease operations in the North African country by June 30. But two of the companies said that if such an edict is issued, they will comply even if it means abandoning assets worth about $1 billion.

Despite reports yesterday from the economic summit in Tokyo that the administration has decided on the June 30 deadline, State and Treasury department officials here said that the future status of the companies was still under discussion. The officials added that they were not aware that any decision had been made or that the United States had promised its West European allies that the firms would be given a deadline for leaving Libya.

The officials insisted that this is the case even though Treasury Secretary James A. Baker III said in Tokyo that the U.S. firms will have to pull out "shortly" as proof that the administration is serious about using economic sanctions to halt Libyan leader Muammar Qaddafi's efforts in support of terrorism. The administration has been embarrassed by European charges that the United States wants the Europeans to take economic action against Libya while permitting U.S. firms to continue operations there.

Some reports from Tokyo also quoted unnamed administration officials as saying the five companies -- Occidental, Marathon, Conoco, Amerada Hess and W.R. Grace -- will have to finish withdrawing by the end of next month. That is the expiration date of special licenses under which the firms were allowed to keep operating after the January implementation of President Reagan's trade embargo against Libya.

The firms, which account for roughly half of Libya's daily export of crude oil, were given the extension after arguing that an abrupt departure in January would have given Qaddafi a "windfall" gift of installations and equipment. Accordingly, the administration allowed the firms to continue temporary operations while trying to arrange sales of their assets to Libyan interests.

Officials in Washington said they expected Reagan and his advisers to use the Tokyo meeting to determine whether the allies would move to prevent European firms from filling the void left by U.S. firms' departure. Some officials also cited speculation that the United States would try to get European countries to curtail purchases of Libyan oil if the U.S. firms were ordered to leave.

In any case, the five companies said yesterday that, except for press reports from Tokyo, they had been told nothing of the administration's plans. However, spokesmen for Conoco and Marathon said they would obey an order to stop operating. The other firms said they could not comment until they had a clearer idea of administration intentions and the legal and financial ramifications.

Officials of some companies, speaking on condition they not be identified, repeated the contention that forcing them to leave before they can sell their assets would cause financial hardships for the firms and save Qaddafi the expense of paying for what they leave behind.

That contention has been disputed by Henry Schuler, a former W.R. Grace manager in Libya who is a research associate at Georgetown University's Center for Strategic and International Studies. He said yesterday that Libya already owns 51 percent of the U.S. firms' operations as the result of past nationalizations, and taxes all but 5 percent of their share of the profits, so "the assets in Libya already are effectively under Qaddafi's control."

Schuler acknowledged that the companies would lose the small fee they are paid for pumping the oil and the large deductions they are able to take on their U.S. income taxes for the taxes paid to Libya. But, he added, the installations that were built in the 1950s and early 1960s already have been used by the companies to take substantial amortization and depreciation tax write-offs and thus cannot be counted as a major financial loss.