In response to a suit brought by the ACLU, a federal district court judge in Washington ruled two weeks ago that the SSS cannot force registrants to give their Social Security numbers at the time of registration.

The SSS had planned to use the numbers to identify registrants and those who failed to register.

Because of the decision--which was based on a violation of the Privacy Act of 1974--the SSS will have to delete upon request a registrant's Social Security number. Selective Service is not expected to prosecute those who refused to surrender their number last summer, when they were required by law to do so.

SSS officials have also refused to discuss their plans for identifying and prosecuting eligible men who refuse to register.

Among the plans under consideration is a cross-checking of SSS files with those of various high schools, colleges and universities, an SSS spokesman said last week.

Men who fail to register face up to five years in prision and a $10,000 fine