The Reagan administration once again is considering a request to Congress to authorize the export of crude oil from Alaska's North Slope.

Senior administration officials say no decision has been made on the controversial proposal. But Lionel Olmer, undersecretary of Commerce for international trade, told a private meeting at the U.S. Chamber of Commerce last week that the administration is planning to seek removal of the ban on exports, according to sources who were present.

Olmer declined to confirm or deny his reported comments. But Mike Mansfield, U.S. ambassador to Japan, suggested in a speech in Tokyo last month that the ban should be lifted. He said this could "dramatically reduce our bilateral trade deficit and increase the value of U.S. exports to Japan by $3 billion to $4 billion per year."

Any attempt to lift the oil-export ban is sure to encounter strong opposition from shipping interests, maritime labor unions, influential members of Congress and some military officers who believe national security requires keeping the oil in this country. When the administration first began considering it as an in-house exercise more than a year ago, scores of senior senators and representatives of both parties put the White House on notice that they would oppose oil exports.

The issue was raised during the recent visit to Washington of Japanese Prime Minister Yashuhiro Nakasone. According to sources familar with those discussions, the administration would like to be able to offer Japan an assured, stable source of oil as a bargaining chip in negotiations over other trade issues. Nakasone and President Reagan agreed to establish a bilateral task force on energy cooperation, and Alaskan oil is one of the items on the group's agenda.

Sen. Ted Stevens (R-Alaska) favors lifting the ban because it would increase the markets for Alaskan crude and stimulate further exploration in his state. Stevens said he discussed it with Secretary of State George Shultz after the Nakasone meeting and came away with the impression that the administration would take no formal position until after the bilateral task force completes its report, probably in mid-March.

Stevens said he doubted that any request to Congress to lift the export ban would be approved if submitted by itself, but he said it might pass if included as part of a comprehensive revision of the Export Administration Act.

That act expires in September. The Commerce Department's International Trade Administration, which Olmer heads, already has begun soliciting advice about what should be included in a new version. Maritime industry officials fear that American-registered tankers would lose business to foreign vessels if the oil were exported. They say they believe the administration hopes to use the Export Act revision to get the ban lifted.

The current worldwide oversupply of oil may have made the idea of exporting American crude more politically palatable than it was in the 1970s. But the most vociferous opposition to crude-oil exports has come from the maritime lobby. So long as the oil coming out of the Alaskan pipeline is shipped only to ports in the United States, federal law requires that it be transported in tankers built and registered in this country and manned by American crews. If the oil were exported, those restrictions would not apply.

The National Maritime Council already has written to Olmer to oppose any attempt to lift the ban. According to the council, permitting oil exports would idle 75 American tankers now used to transport Alaskan crude.

Stevens said, however, that the new export law could be written to equire that crude oil from existing wells, at least, be exported in U.S.-flag vessels. Mansfield said he had "received the impression" from Japanese executives that they would be willing to accept such a restriction.