Senators pushing legislation to require young men to register with draft boards have called off their effort until next year, Sen. Sam Nunn (D-Ga.) said last night.

Nunn said in an interview that he would voice the case today in a closed session of the Senate for resuming draft registration but would not put the politically explosive issue to a vote.

This represents a change in his legislative strategy. Nunn originally planned to put his bill, which would require men 18 through 26 to register with draft boards starting next January, to a vote this year.

"The House has shown that calling up the registration bill this year would be an exercise in futility," Nunn said. The reference was to last week's 252-to-163 House vote against registration.

he Joint Chiefs of Staff have recommended resuming registration to make it easier to respond swiftly to a national emergency or a war.However, President Carter said the step is not needed at this time.

Congressional backers of registration and the draft have figured all along that they would have an uphill fight until after the November 1980 elections.

Nunn denied last night that he was trying to capitalize on a pro-defense mood in the Senate by making the case for resuming registration so soon after Tuesday's vote to increase defense spending.

"I would have preferred to discuss it next week," he said.

David Landau, vice chairman of a coalition, of national organizations that oppose registration and the draft, accused Nunn of "continuing to push registration in secret rather than bring it out in the open."

He said senators will get a "distorted" view of the registration issue because outside opponents will not be able to marshal effective challenges.

Nunn said he asked for a closed Senate session because the Defense Department refused to declassify information needed to understand the need for compulsory registration. He said he will push for a vote on the issue next year.

Today's closed session, Nunn said, will focus on the nation's "poor" mobilization condition. It will take too long to register, classify, draft and train recruits under present circumstances, he said.

A Pentagon mobilization exercise called Nifty Nugget spotlighted many shortcomings that Nunn intends to discuss today.