AZT, the most common drug used against the AIDS virus, has been dropped from a clinical trial among children after it proved to be the least effective and to cause the highest rate of side effects.

The National Institutes of Health announced Monday that the AZT part of a clinical trial testing three drug strategies for treating children with HIV has been discontinued. The other two arms of the study will continue.The clinical study, started in 1991, was testing AZT alone, AZT with ddI, another antiviral, and ddI alone, in the treatment of children from the ages of three months to 18 years. All of the patients were infected with the AIDS virus.

A review board recommended discontinuing the AZT arm after it was shown that children receiving this drug alone had a more rapid progression of disease than did children receiving the other two drug therapies.