That ''argument of entitlement,'' as Mrs. Smeal calls it, was one of the factors that persuaded her that exclusion from the draft hurt the interests of women.

''Men are at risk in a way that women are not,'' she said. ''That risk entitles men to certain privileges and benefits.'' Ever since ancient Egypt, she said, ''the secondary class has not been given the right to serve in the military.''

By excluding women even from registration, Mrs. Smeal continued, ''the Government says that every man, regardless of any disability, must register, but that all women, regardless of competency, cannot.'' The distinction creates the ''myth that all men are more competent than all women,'' she said, adding, ''It's a major institution of our society saying: 'You can't cut the mustard.' ''

The National Organization for Women's brief cites a number of internal military studies showing that women, who now make up 8 percent of the armed forces, generally perform well. The Department of Defense told Congress in 1979 that women, when ''properly trained and selected, have the physical and mental ability to serve in the entire range of military classifications.'' 'Devastating' Harm Found

''Compulsory universal military service is central to the concept of citizenship in a democracy,'' the brief filed by NOW asserts. The brief says that ''devastating longterm psychological and political repercussions'' result from the exclusion of women ''from the compulsory involvement in the community's survival that is perceived as entitling people to lead it and to derive from it the full rights and privileges of citizenship.''