President Carter has stopped trying to block the Navy's nuclear-powered aircraft carrier in exchange for a congressional cease-fire on efforts to lift economic sanctions against Rhodesia.

This means, administration officials said yesterday, that the Navy will be allowed to build another Nimitz, costing $2.36 billion, even though the president vetoed last year's defense bill on the ground that building another nuclear carrier would be a waste of money.

"The president threw in the towel because there were just so many battles he could fight at once," one administration official said yesterday.

After the Senate Armed Services Committee had rejected Carter's request for a small, conventionally powered carrier and authorized instead the construction of an oil-fired Kennedy-class carrier to cost $1.8 billion, the administration told the House it would settle for the Kennedy.

However, by lopsided votes last month the House rejected attempts to delete the nuclear-powered Nimitz from the Pentagon's Fiscal 1980 authorization bill. This pitted the Nimitz against the Kennedy in the House-Senate conference on the rival defense bills.

Last week, administration officials said they would go along with the Nimitz if the conference eliminated language in the Senate money bill requiring the president to lift import restrictions on strategic and other materials from Zimbabwe-Rhodesia. Sen. Harry F. Byrd (Ind.-Va.) championed that provision.

The conferees agreed to do this, substituting generalized language in the compromise money bill stating that it was the sense of Congress that the United States should be able to import critical materials "without artificial impediments."

In a separate action, the conferees on the $42 billion procurement authorization bill agreed to build two nuclear attack submarines of the 688 class rather than the one which Carter requested.

The House on Friday passed a defense bill appropriating $129.9 billion for the Pentagon for Fiscal 1980. The Senate has not yet passed its defense appropriations bill.

Asked if Carter intended to try to cut off money for the Nimitz during the coming House-Senate conference on the appropriations bills, on administration official said yesterday no such fight is contemplated.

"You're going to have to pay the extra for the Nimitz," he said. Adm. H. G. Rickover and his congressional allies contended the Nimitz was worth the difference.

The House failed to override Carter's veto of the Nimitz last year. But Carter apparently did not want to put his strength to the same test this year in light of the congressional demands for higher defense spending.