WASHINGTON--In a recommendation that could affect millions, the Public Health Service recommended yesterday that all people in high-risk groups undergo periodic blood tests to check for infection by the AIDS virus.

While there remains no cure for AIDS, agency officials said, research over the past year shows that virtually all people in high-risk groups who repeatedly test positive to the blood test can infect others.

Thus, they said, people with verified positive results can be counseled on how to avoid spreading the deadly disease to others, particularly including sexual partners.

"The thrust of these recommendations is that we're saying, have this serological [blood] test," said Dr. Donald R. Hopkins of the federal Centers for Disease Control.

"We have great confidence in this test," Hopkins said. "And it's increasingly obvious that a large part of the problem...is represented by people who are infected but who are not now symptomatic."

"Most such people that test positive are infectious, intermittently or permanently," he said. "We think it's important for them or their partners to know whether they are positive or not."

The recommendation was announced at a news conference by Hopkins, federal AIDS coordinator Walter R. Dowdle and Dr. Harry M. Meyer of the Food and Drug Administration.

None of the three could say how many people were covered by the recommendation. Hopkins, under intense questioning, estimated it might be between 10 million and 20 million. But Dowdle said such figures are speculative and are largely irrelevant because many people will not comply.

High Risk List

"We don't really expect there to be a stampede," he said. But, Dowdle added, "we certainly hope there will be."

But the potential figure clearly is in the millions.

The government's list of high-risk populations includes homosexual or bisexual men, a figure which some have estimated at 10 percent of the male population.

Others include past or present intravenous drug abusers; people born in countries where heterosexual transmission of AIDS is considered common, including Haiti and Central Africa; male or female prostitutes and their partners; sex partners of high-risk individuals; hemophiliacs who have received blood clotting-factors; and newborn infants of high-risk or infected mothers.

In other recommendations, the agency urges people who test positive to inform their sexual partners of the result and refer them for their own test and for counseling.

It also endorses efforts by state or local officials to regulate or close facilities that encourage high-risk behavior, such as "bathhouses" for homosexuals, houses of prostitution and the "shooting galleries" of drug addicts.