One in three Americans thinks people can get AIDS by donating blood, an erroneous belief that has led to a dangerous shortage of blood in the nation's blood banks and to the popularity of private donations.

These findings came from a survey released last week by the American Association of Blood Banks, which said the fear is one reason that blood banks are operating at up to 13 percent below normal levels.

"The fear goes against all scientific evidence," said Gilbert Clark, executive director of the 2,300-member association. The association, along with local branches of the American Red Cross, collects and distributes nearly all of the blood products used in the United States.

"You cannot get AIDS by donating your blood," Clark said.

But because AIDS can be transmitted through blood, Clark said, the public becomes fearful of anything involving blood.

Less than half the people surveyed knew that the nation's blood banks test and screen all blood for antibodies to the virus that causes acquired immune deficiency syndrome. Before the test was approved by the Food and Drug Administration in the spring of 1985, blood contaminated with the virus was received by an unknown number of patients.

A total of 252 adults and 34 children in the United States have contracted AIDS through blood transfusions, according to Jan. 6 figures compiled by the federal Centers for Disease Control. None of the cases was contracted from blood transfused after the screening test came into use, according to federal officials.

The new test is highly effective, but not 100 percent fail-safe, because there is a four- to six-week period after infection with the AIDS virus before antibodies emerge.

"There is a window of time if you're infected with the virus," said Dr. Eugene Berkman, president of the American Association of Blood Banks and professor at Tufts University School of Medicine. "There are people who may have just got infected yesterday who could donate."

But the possibility is remote, he said, because people in high-risk groups are choosing not to donate. "Self-selection works," he said, citing studies that show that among blood donors, the percentage of people who test positive for AIDS antibodies is lower than that of the general population.

Although the blood banking industry says the screening and self-selection have made the public blood supply safer than ever, an overwhelming finding of the survey was that people strongly support directed donations, a procedure in which friends and relatives donate blood for a selected patient rather than into a universal pool.

Eighty-one percent of those polled said they would prefer to receive blood from friends or relatives, a practice that hospitals traditionally have discouraged.

"We think the general population blood is safer," said Dr. Ron Sacher, blood bank director at Georgetown University Hospital. "We tend to be much more critical of directed blood" because relatives and friends could conceal health problems.

Dr. Paul McCurdy, director of blood services for the Red Cross in the Washington region, said he was aware of two cases in which sons donated blood at the request of their mothers, who were unaware their sons were homosexuals. Homosexual men are a high risk group for AIDS and are asked to refrain from donating blood. Their blood tested positive when screened for the AIDS virus antibodies and was rejected, he said.

"Directed donations are coercive," McCurdy said. "After someone asks you and you don't want to, there will always be a question later of why."

But public pressure has prompted many hospitals and blood banks across the country to allow directed donations. One of the largest programs is at Irwin Memorial Blood Bank in San Francisco, a city with the second-highest number of AIDS cases.

Directed donations also reduce the blood supply, according to McCurdy and others. "It's trouble because people are holding back their donations to save themselves for friends and relatives," said McCurdy.

Education of potential donors eases some fears. Half of those interviewed for the blood donation survey said they were more likely to give once they knew that all needles are sterile, are only used once and carry no risk of transmitting AIDS.

The polling firm, Hamilton & Staff of Chevy Chase, concluded that "the public's concerns over AIDS are much more emotional than factual."

To allay fears, the American Association of Blood Banks plans to use films and public service announcements on television and radio to give the message that donating blood does not expose people to AIDS.