A top government scientist was barred from speaking at a conference sponsored by the nation's first test-tube baby clinic because his boss feared the speech might violate a federal ban on funding such facilities.

Dr. Gary Hodgen, 39, chief of the pregnancy research branch at the National Institute on Child Health and Human Development said Dr. Mortimer Lipsett, head of the institute, told him on Thursday, three days before the start of the conference, to cancel his appearance.

The meeting, which opened Sunday in Norfolk, is sponsored by the Eastern Virginia Medical School, which last year produced this country's first test-tube baby. The workshop, which Hodgen was to have addressed today, has attracted 200 physicians and scientists.

Hodgen, the only federal official who was to have spoken at the conference, said yesterday that his planned talk did not deal specifically with in-vitro fertilization, the scientific name for test-tube conception, but with "tangentially related research opportunities" that could ultimately lead scientists to understand what causes genetic birth defects.

Lipsett, recently appointed by Health and Human Services Secretary Richard Schweiker to head the Bethesda institute, part of the National Institutes of Health, said his decision stems from a 1974 moratorium on federal funding for test-tube baby projects. In 1979 a federal Ethics Advisory Board recommended an end to the ban on funding laboratory efforts to create human life.

That ban, Lipsett said yesterday, remains and "we're still living under that. Therefore I didn't think it was wise for him Hodgen to speak."

In recent years clinics, including the privately funded one in Norfolk, have come under fire from right-to-life groups who claim that test-tube conception represents scientific tampering with human life.

"Dr. Hodgen understood my decision. He knows this is a sensitive area," said Lipsett, who added that he did not consult Schweiker or other top HHS officials because "I didn't feel I had to. This was a sensitive area in the last administration, it's a sensitive area now . . . Don't ask me to debate policy or discuss my personal feelings, please."

Hodgen said he was invited to the conference several months ago by Dr. Howard Jones, a member of the husband-and-wife Norfolk team that achieved the first American birth of a child conceived through an in-vitro fertilization. Hodgen said he accepted the invitation and then routinely informed his superiors that he planned to attend the conference.

"Dr. Lipsett said it might be against the spirit of the earlier ruling," said Hodgen, an endocrinologist well known in his field for his work on female reproduction. "Dr. Lipsett felt that a conservative decision was the right one and I support that."