WASHINGTON, D.C., March 3--Delegates to the National Student Association conference at American University today overwhelmingly endorsed the idea of a National Service Corps, but expressed serious reservations on several key issues.

The conference defeated by a vote of 78-8 a motion by the National Student Committee for Effective Social Welfare which requested "abandonment" of the Service Corps proposal.

The committee, composed almost entirely of members of Young Americans for Freedom, charged that the conference had been presented a "thoroughly contradictory...and in general an incomprehensible exposition." The committee listed nine students as members--one more than voted for its resolution.

After hearing reports by Secretary of the Interior Stuart Udall, officials of the President's study group and others, the delegates at the plenary session today voiced strong objections to the vagueness of current thinking on certain features of the National Service Corps.

Richard Boone, a member of the President's study group, said yesterday that either state and municipal governments or private organizations would be able to request help from the Corps.

Southern Obstruction

Under questioning, however, Boone could not state definitely whether Southern states or Congressmen, for instance, could stop Service Corps projects in their area. Such projects, by improving Negro education, could possibly shift the balance of electoral power.

Dennis Shaul, president of NSA, said in a speech to the conference that the Service Corps would not be able to undertake projects that would involve important "social change." He asked that present ambiguity on the question of control and administration of projects receive further study.

Retraining of Workers

Another criticism made by Shaul, and echoed by delegates at the plenary session, was that present proposals avoided the problem of the retraining of unemployed workers.

In general there was little heated debate on the floor of the conference this afternoon. Except for several crippling motions proposed by the Committee for Effective Social Welfare, which were all defeated, few delegates attempted to amend the resolution that had been produced by three days of workshop session.

The delegates approved 17 resolutions dealing with the structure, administration, and aims of the National Service Corps. Many indicated their willingness to serve after the Service Corps proposal receives Congressional approval. A member of the President's study group said that over 75 per cent of 10,000 college students contacted by his office said they would consider joining the Corps.