The Reagan administration said yesterday it reserves the right to keep some of its Pershing nuclear missiles in Europe by reducing their range and transferring them to the West German government, even after a deal is made with the Soviet Union to ban intermediate-range missiles in Europe.

State Department spokeswoman Phyllis Oakley announced the U.S. position after discussion of such a plan in Bonn Wednesday by Maynard W. Glitman, chief U.S. negotiator for intermediate-range missiles at the Geneva arms talks between the United States and the Soviet Union.

It was widely anticipated that the Soviet Union will reject such a U.S. plan. A senior Soviet official in Washington said that while the embassy has not received an official stand from the Kremlin, Moscow will object to any such transfer in strong terms.

The drive toward agreement on a treaty banning intermediate-range and shorter-range nuclear missiles from Europe has been interrupted in recent weeks by Soviet demands to include Pershing IA shorter-range missiles already in the hands of the West German government. The United States, which controls the nuclear warheads on these weapons, has insisted that they not be covered by the treaty.

The latest U.S. statements suggest to some officials that Washington is creating a chip that in final bargaining it can trade off against the Soviet demand that German Pershing 1As be included. Other officials said the statements flow logically from U.S. backing for the modernization of the German Pershing IAs that was a condition of NATO's approval of the U.S. bargaining position at Reykjavik, where NATO foreign ministers met earlier this month.

Specifically, spokeswoman Oakley said the U.S. "draft treaty" that has been proposed at Geneva would permit the conversion of U.S. Pershing IIs, which have a range of about 1,100 miles, to Pershing IB missiles with a range of about 400 miles. She went on to say that under "a long-established program of cooperation" with Bonn, the United States could then transfer those weapons to West Germany.

State Department sources said U.S. negotiators contended in Geneva that the Soviet Union could not similarly convert and transfer any of its medium-range missiles in this way because there is no "long-established program" under which Moscow shares nuclear missiles with its allies.

Oakley said the U.S. position on this issue is "hypothetical" because "there is currently no U.S. or West German proposal" to convert the weapons, although the United States is demanding the right to do so. White House spokesman Marlin Fitzwater said "we don't have any plans" to convert the Pershings as permitted by the U.S. position.