The White House yesterday rejected Leonid I. Brezhnev's call for an immediate freeze on the deployment of new nuclear weapons but welcomed the Soviet leader's "announced willingness to begin negotiations on substantial reductions in strategic nuclear arms."

This was the White House's second reaction to the new Soviet proposal. Earlier, President Reagan, responding in jest to a reporter who asked if he had a reply to Brezhnev's proposal for a freeze, replied: "Not that you'd want to print." Then he added, "I'm kidding. I think we'll be meeting."

The White House later explained that Reagan meant that the two governments would be meeting to discuss arms control, not that Reagan and Brezhnev would have a personal encounter.

In effect, in this latest round of public diplomacy, each superpower has now taken what it liked from the latest proposals of the other, while rejecting the substantive proposals. Brezhnev rejected the proposals Reagan made in his May 9 speech at Eureka College in Illinois, but welcomed his willingness to negotiate. Yesterday Reagan gave the same reply to Brezhnev's substantive response to his Eureka proposals.

Administration officials expressed hope yesterday that the upshot of this public exchange would be an early beginning to real negotiations on limiting nuclear arms. Some officials are hopeful that the talks could begin next month, when Secretary of State Alexander M. Haig Jr. could meet at the United Nations with Soviet Foreign Minister Andrei A. Gromyko.

Brezhnev seemed to have western public opinion very much in mind yesterday when he called for a freeze on nuclear weapons, an idea that has attracted a wide following both in the United States and Western Europe. But the principal political backers of a freeze in this country immediately distanced themselves from the Soviet leader's version.

"The Soviet proposal is not the kind of freeze that we favor," said Sens. Mark O. Hatfield (R-Ore.) and Edward M. Kennedy (D-Mass.), co-sponsors of a Senate resolution calling for a freeze on the testing, manufacture and deployment of nuclear weapons. The Brezhnev idea "appears to be a limited proposal which applies only to the deployment of new nuclear weapons systems, of which the United States has more on the drawing board than the Soviets do."

But if politicians involved in the American freeze campaign felt they couldn't endorse a Soviet idea, other Americans backing the freeze endorsed it warmly.

"I think we should take him up on it," said Randall Forsberg, one of the originators of the freeze idea and a leader of the campaign. If the Reagan administration rejects Brezhnev's proposal, she added, that would put the United States in the position of "unilaterally" prolonging and aggravating the arms race.

Jeremy J. Stone, executive director of the Federation of American Scientists, said the Brezhnev proposal "is really a pretty good formula" because it would allow for negotiating some continued qualitative improvements in U.S. forces while putting a numerical cap on the strategic-weapons competition. Stone said "this is an historic opening in the arms race" to actually cut off the escalating arsenals of both superpowers.

Rejecting the freeze idea explicitly, the White House repeated its belief that "a freeze now would codify existing Soviet military advantages" and would "remove Soviet incentives to agree to the substantial reductions which President Reagan has identified as our primary objective." The administration wants to use the threat of a continuing American strategic buildup as a bargaining chip in the coming negotiations.

The White House dismissed as unacceptable references in Brezhnev's speech to freezing nuclear weapons in Europe.

But a range of administration officials including Haig, Vice President Bush and arms control director Eugene V. Rostow publicly welcomed the Soviet leader's apparent willingness to start arms talks soon. All said they hoped for early negotations.

Rostow described Brezhnev's freeze offer as "a grandstand play that's perfectly consistent with their policy of trying to freeze in a position of strength.