A panel of prestigious education researchers warned yesterday against giving national or statewide minimum competency exams to high school seniors, saying so many would fail a respectable test that it would be "politically unacceptable."

Proposals have been pushed in more than half the states and in Congress in recent years to require that students pass certain minimum tests before being promoted or given diplomas. The idea is to keep the schools from being conveyor belts in which promotion and graduation are automatic.

But the panel, created at the request of Health, Education and Welfare Secretary Joseph A. Califano Jr. last year, said imposition of any high standard on current high school seniors would be unfair, and simply document "accumulated deficits," particularly among blacks and other minority-group members.

If the standard of the graduation test was low enough to prevent widespread failures, the panel said, it would be "meaningless" and might only encourage a further decline in academic achievement.

The group declared, however, that there was "substantial merit" in having states experiment with competency exams in lower grades.

In an interview, Stephen K. Bailey, Harvard education professor who was the panel's chairman, said he personally favors "phasing in" statewide minimum competency exams with youngsters now entering first grade so they would be required to master definite skills before they are promoted through their 12 years of school.

"That way we can catch people early and deal with their problems," Bailey said. "I'm strongly against automatic promotions except when we talk about those in the last year of high school and impose something then as a penalty that they can't possibly meet."

In its report, the panel said requiring seniors to pass a statewide or national test now to get their diplomas "will create more social problems than it can conceivably solve. . .

"If success on tests. . . is achieved by four fifths of a suburban school system, but only one third of a central city system," it said, "the consequences could be serious for domestic tranquility as well as social equity in a world where a high school diploma, regardless of intrinsic meaning, is frequently a ticket to particular jobs."

The panel's report was made public at a national conference on achievement testing and basic skills, sponsored by HEW. About 350 persons -- including state and federal legislators and education officials -- attended the meeting yesterday at the L'Enfant Plaza Hotel.

Califano told the session that the Carter administration strongly opposed having the federal government help establish any national competency tests, as provided by several bills now before Congress.

Even if the tests are voluntary, he said, they would "improperly centralize a matter of educational policy that has traditionally been a matter of state and local control."

But Califano said the administration would seek funds from Congress for states to develop demonstration projects in competency testing.President Carter, he said, "is very enthusiastic about this subject."

In the afternoon, John Ryor, president of the National Education Association, the country's largest teacher group, denounced as unfair any tests that permit comparisons of students in different school districts.