THE SKIES OVER WASHINGTON are full of trial balloons these days. The Reagan administration hasn't even decided - officially - if it will introduce its own trade bill. Already, however, major provisions are being wafted upward. Among them:

* A $200 million fund to subsidize loans to developing countries to help them pay for imports of U.S. goods.* Changes in the antitrust laws permitting companies threatened by import competition to merge.

* Revisions in the laws governing unfair trade practices permitting the government to bar imports that violate such intellectual property rights as copyrights, patents and trademarks.

* Extension of the rules governing countervailing duties applying to countries dumping or selling goods below cost.

* Extension of the government's authority, which expires next January, to negotiate reductions in tariffs and quotas under the 90-nation General Agreement for Tariffs and Trade. The authority is needed to permit the United States to participate in the so-called Uruguay round of GATT talks, which are expected to begin next month.

No one in the administration would say there is enough red meat in these proposals to satisfy members of the new 100th Congress, both houses of which have a Democratic majority. Even some Republicans are going to be hard to satisfy.

Frank H. Murkowski, GOP senator from Alaska, told a university audience recently, for instance, that it's time to blast open markets overseas that have remained closed to U.S. exporters.

His proposal? Keep Japanese construction concerns from bidding on the $25 billion of Federal Aviation Administration projects in the United States as long as U.S. companies are excluded from the $8 billion Kansai Airport projects in Osaka Bay. That's one example.

Sen. Murkowski hinted that Japanese political leaders might even welcome such a threat. Preliminary announcements indicated the Japanese would consider proposals from bidders outside Japan. But pressure from the construction industry and its close ally, the labor unions, changed the message to read: ''No foreigners need apply."

If Japanese political leaders were able to make a convincing case that the nation's exports, upon which its economy depends so heavily, were in real jeopardy, some progress on U.S. access might be possible. There is no doubt, however, that whatever trade bill emerges from the new Congress, it will have to address the problem of access.

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