The Reagan administration yesterday unveiled proposed rules that would require young men to prove they had registered for the draft before they could receive federal student aid for the 1983-84 academic year.

The rules would implement a law passed by Congress last summer that prohibits draft resisters and other nonregistrants from getting direct federal educational aid or federally guaranteed student loans.

"The law is clear and the government will carry out its responsibilities fairly but firmly," Education Secretary Terrel H. Bell said. "The message is simple. No registration, no student aid."

Under the rules, a young man would have to show college loan officers a letter of acknowledgement from the Selective Service that he had registered, or an affidavit saying verification would be provided in 120 days. If that period passed without further documentation, the student would be considered in default of the money he had received.

The proposal suggests that all students be given a Statement of Registration Compliance, with a section where they could indicate why they didn't have to register.

One of the five reasons listed would be a student's sex, since women are not required to register under the Selective Service law. Two others involve age, since only those men between 18 and 21 are required to register.

The constitutionality of the law has been challenged in the U.S. District Court for Minnesota by the American Civil Liberties Union and the Ralph Nader-founded Minnesota Public Interest Research Group. A decision is pending, ACLU Washington office director John Shattuck said yesterday.

"These are highly punitive actions taken against a whole class of people--essentially it's using the process of student loans to punish draft resisters and we think it's a highly irregular and constitutionally dubious approach to the problem," Shattuck said.

"There are very important constitutional issues . . . ," said John B. Jones Jr., a Washington attorney for the American Council on Education, a group representing 1,500 colleges and universities. ". . . There's a special problem for certain religious colleges that have a pacifist tradition and on completely extraneous ground are being forced to participate in the military."

Bell estimated yesterday that 2.5 million students will apply for federal financial assistance in the coming academic year. No estimates were immediately available of the number of those students who are required to register for the draft.

As of Jan. 1, about 5.7 percent--or more than 500,000--of the 9.8 million eligible young men had not registered for the draft.

"We feel it's a bad law so whatever the regulations say isn't going to make it any better," said Judy Schnidman, special projects director of the United States Student Association. " . . . We'll continue in our efforts to get the law repealed."

David J. Hoy, director of student financial aid at Haverford College in Haverford, Pa., said he had not yet read the proposals but understood they "would make the schools the gatekeeper . . . the police for the students. We're the ones who are going to have to tell them, in some cases, 'You can't go to college.' "

Hoy, a member of a new ACE committee on draft registration, added that the proposals would inevitably add to existing delays in processing loan and aid applications, delays he said have been exacerbated by paperwork requirements that the administration has added in the past two years