Deputy Secretary of State Kenneth W. Dam has told Social Democratic Party leaders here that the United States has no intention of seeking to deploy medium-range nuclear missiles earlier than planned in order to preempt potential West German political opposition.

Dam said that he had provided the assurances Friday at the request of the opposition Social Democrats during a biennial meeting of West German and U.S. governmental and private leaders.

Dam, U.S. arms negotiator Paul Nitze and Assistant Secretary of Defense Richard Perle were among the U.S. participants in the meeting, which ended late Saturday. All have had important roles in making Reagan administration arms policy.

When they were leading the government in 1979, the Social Democrats backed the original decision to plan to deploy Pershing II and cruise missiles in Western Europe to counter a buildup of Soviet medium-range missiles. The conservative Christian Democrats took over the government in October, however, and now the Social Democrats are believed to have been moving steadily away from their earlier support.

The Social Democrats are not likely to adopt a new position until the party convention in late October or early November, just a few weeks before scheduled deployment of the Pershings. Concern has been expressed in the party that the missiles might be installed early, but Dam assured leaders here that such a "preemptive deployment" would not be undertaken before the party works out its position.