Selective Service Director Bernard D. Rostker said yesterday that 93 percent of all affected men registered for the draft in the first month after the nation's new registration program began July 21.

Rostker said the 93 percent -- 3,593,187 registrants out of the estimated pool of 3,880,000 eligible men aged 19 or 20 -- was substantially greater than the 83 percent that registered in a similar period in 1973, the last year for which full figures under the old registration system are available.

The draft was suspended late in 1972, and registration was stopped in 1975. President Carter requested reinstatement of registration, but without any immediate plans to revive the draft, in his State of the Union Message this year.

Declaring himself "not unhappy" with the 93 percent turnout, Rostker said the registration was so high because "basically, 19-to 20-year-olds are patriotic, law-abiding citizens, and they heeded the lawful call of the president and the Congress."

Rostker said only 1.8 percent of those who registered has written onto the form some indication that they were conscientious objectors or were otherwise registering under protest.

The 93 percent turnout was far higher than had been precidted by some antidraft groups, who said youths would decline to sign up, and later yesterday the Rev. W. Barry Lynn, director of the Committee Against Registration and the Draft, challenged the Rostker figures.

Lynn said the 50-organization antidraft group that he heads knew of many youths who had filled in "Don Duck" or "Michael Mouse" or other fictitious names -- one youth claimed he turned in 106 cards with fictitious names -- and that these obviously hadn't been deducted from the 93 percent.

Lynn said the 93 percent result was completely at variance with surveys by The Boston Globe, his organization and others showing that only "75 to 80 percent" of eligible registrants had signed up.

Lynn repeated demands that the registration program be called off, and said that even if the 93 percent figure is correct, it still "makes criminals of the 250,000" who haven't registered and therefore can face fines and jail terms. He said the General Accounting Office should check Rostker's figures.

A Selective Service spokesman responded later that officials "can't imagine that the number of those signing Michael Mouse or Don Duck" would turn out to be high enough to significantly affect the signup proportion -- far less than 1 percent according to preliminary checks.

Rostker, saying 93 percent is a "very hard" figure, gave this breakdown of eligibility versus signup:

All told, based on Census Bureau figures, there were 4,310,000 men 19 or 20 subject to registration. About 60,000 were institutionalized in hospitals or prisons, and another 370,000 were already members of the armed forces and therefore exempt. This leflt 3,880,000 as the base population subject to registration.

In the initial July 21 to Aug. 1 open signup period, 87 percent of these men had signed up (registration took place at post offices), and in the next three weeks, ending Aug. 22, another 6 percent signed up for a 93 percent total, or 3,593,187.

He said the figures reflected names punched into a borrowed Internal Revenue Service computer system based on cards turned in by registrants, plus a handful of added cards that came in to Selective Service.

In 1973, he said, 77 percent had signed up on time, and another 6 percent within another month, for a total of 83 percent, so the 1980 registration had a better result. He added that in 1973 the figure had reached 97.4 percent after one year as latecomers straggled in, and he expected that 1980 would come close to 98 percent after more time has passed.

He added that while prosecution of non-signers could occur, nobody could be prosecuted until at least 90 days after the signup period closed and after letters of confirmation had been sent to registrants. "At present we are till taking later registrations, not prosecuting," he said.