A record 71 deaths from acquired immune deficiency syndrome (AIDS) were reported in San Francisco for April, three more than the previous monthly high set in March. Ninety new AIDS cases were recorded in April, trailing only the 101 new cases recorded in February.

The figures reflect "what was happening some time ago, not the transmission of new infections now," said Dr. Dean Echenberg, the city Health Department's communicable disease chief.

Echenberg said that about half the city's estimated 80,000 homosexual men are infected with the AIDS virus, which can be spread by some forms of sexual contact, contaminated needles or contaminated blood products. The city's total population is just over 700,000.

Health officials said homosexual men account for 97.4 percent of San Francisco's AIDS cases.

In New York City, an average of 239 new AIDS cases was reported monthly for the first three months of 1986, up from a monthly average of 214 new cases for the last six months of 1985, according to that city's Health Department.

In the nearly five years that such records have been kept, 1,959 AIDS cases and 1,094 deaths from the disease have been in San Francisco. The Centers for Disease Control in Atlanta shows 20,088 cases and 10,800 deaths in the nation as of April 28.