The Reagan administration formally announced yesterday that it is giving some U.S. companies operating in Libya temporary "exemption licences" allowing them extra time to sell their assets. At the same time, it took new steps to increase the pressure on them to adhere to U.S. economic sanctions imposed on that country last month.

The licenses, according to two senior administration officials, are being granted "in exceptional cases" to prevent Libyan leader Muammar Qaddafi from reaping a "potential economic windfall" of $1 billion or more as the result of forced sales -- particularly of oil company assets to the Libyan government.

Meanwhile, Pentagon sources said the U.S. aircraft carriers Coral Sea and Saratoga and their supporting warships have ended port calls in Trieste and Naples, Italy, and begun heading toward the central Mediterranean waters north of Libya where they conducted maneuvers in late January. They are expected to arrive there on Monday.

A third carrier, the America, was issued orders to depart from Norfolk and enter the Mediterranean in late March.

The America is expected to replace the Saratoga, although it was not clear how long the three ships would be in the Mediterranean together.

Qaddafi claims the disputed Gulf of Sidra is within Libyan territorial waters and has sworn to defend it. A U.S. official said the ideal time to enter the Gulf would be when all three carriers were on station.

The administration also announced yesterday it has decided to take no action against American citizens married to Libyan nationals out of the "humanitarian consideration" to "preserve family unity."

In early January, the administration imposed economic sanctions on Libya, ordering U.S. firms to cease doing business there and the estimated 1,500 American residents to leave by Feb. 1. U.S. officials think that most U.S. citizens have left, except for an estimated 200 to 300 wives of Libyans.

The administration has been seeking to work out a compromise with U.S. companies -- which stand to lose $1 billion to $6 billion in oil, assets and business -- so they will not be forced into "fire sales" from which the Libyan government would benefit.

The temporary "exemption licenses" the administration is offering entail harsh conditions that include an obligation to end all dealings in Libya "as soon as practicable on fair and appropriate terms" and the placing of profits in an escrow account under U.S. control.

The money would be released only after each firm terminates its activities in Libya "and as agreed by the U.S. government."

The administration officials said 15 or 16 firms had applied for the licenses and that those for the five American oil firms operating in Libya were available immediately.

The five oil firms -- Occidental Petroleum, Conoco, Marathon, Amerada Hess and Grace Petroleum -- face additional conditions to obtain an extension license, however.

The regulations issued yesterday said the firms must end their involvement in operating Libyan oil fields; not distribute Libyan oil through their transporation and refining networks; sell their share of Libyan oil in Libyan ports and not elsewhere; undertake no new activities or obligations and hold existing activities to a minimum.

Occidential spokesman Frank Ashley said the company was "pleased" the new guidelines "appear to provide a framework for complying with the president's directive without forcing a sacrifice of the property of our shareholders and our allies." He refused to comment further.

A Marathon spokesman said his company had reached no decision on selling its Libyan assets and was waiting to examine the language of the exemption license before commenting further.