Screening of the nation's blood supply for a leukemia-causing retrovirus related to the AIDS virus should begin as soon as a test for it can be licensed, according to researchers who today reported evidence of the viral infection in the blood of six patients who had received numerous transfusions.

"I believe it {screening} should be done nationally," said Dr. Donald Armstrong, chief of the infectious disease service at Memorial Sloan-Kettering Cancer Center in New York and one of the authors of the new report. "I don't want to transfuse any virus into anybody, particularly if that virus is associated with leukemia."

The virus, known as human T-cell leukemia virus or HTLV-1, infects as many as 15 percent of healthy persons in some areas of Japan, which has a national program to screen all donated blood. The virus can cause a type of leukemia, a neurological disorder with symptoms similar to multiple sclerosis and immune system abnormalities. Apparently only a small percentage of those infected ever become ill, but studies indicate the virus can remain dormant for as long as 30 years before producing symptoms.

"There's no question that there's more than one retrovirus that we have to be concerned about," said Dr. Samuel Broder of the National Cancer Institute, who wrote an editorial accompanying the report in today's New England Journal of Medicine. "It makes sense to me to develop a method for screening blood-bank donations" as is done for the virus that causes acquired immune deficiency syndrome.

Evidence of infection with HTLV-1 was found in blood samples saved from six of 211 leukemia patients who had been treated at the Manhattan hospital. All patients in the study had received dozens of transfusions.

None of the infected patients had the type of leukemia caused by the virus, and all had died of their cancer by the time the study was done. The earliest blood sample showing evidence of infection dated from November 1976.

Serial specimens from three of the infected patients showed that the test turned positive during their hospital treatment, suggesting that the infection occurred through a transfusion.

At least two companies have applied to the Food and Drug Administration to be licensed to conduct blood tests for HTLV-1. An FDA spokeswoman said the agency is evaluating the tests' accuracy but that approval is not expected soon. A test "may be approved this year," she said.

The country's major blood-banking organizations have taken the position that the need for a national screening of blood for the virus is not scientifically proven because there has been no reported case of a patient developing leukemia as a result of a transfusion.

But Dr. James P. AuBuchon, a medical officer with the American Red Cross, said in an interview Tuesday that a national screening program should begin as soon as a blood test is licensed.

An American Red Cross study of about 40,000 blood donors in eight U.S. cities found 10 whose blood contained antibodies indicating infection with HTLV-1, a frequency of .025 percent. Armstrong said he and his co-workers, using the results of their study, estimated a similar infection rate, .023 percent.

Other studies of U.S. blood donors have found higher infection rates: 1 percent in a National Institutes of Health study, and 2 to 3 percent in Birmingham, Ala., and Houston. Infection rates with HTLV-1 are higher in the southeastern United States than in other regions.

A variety of leukemia affecting a type of white blood cells called T-cells apparently develops in less than 1 percent of persons infected with the virus, often after a long, symptomless incubation period, Broder said. He said the virus can also cause a neurological condition with symptoms of muscle weakness or paralysis similar to those of multiple sclerosis.

Like the AIDS virus, HTLV-1 can be transmitted through sexual intercourse and by an infected mother to her infant. It apparently can also spread among drug addicts through sharing of contaminated needles.