President Carter, leading off an administration effort to solidify public support behind the new strategic arms limitation treaty (SALT) with the Soviet Union, warned yesterday that rejection of the accord would be a "devastating blow" that would leave the United States looking like a "warmonger" to the rest of the world.

At the same time, the administration put into motion a high-powered public relations campaign designed to capitalize on public interest in the treaty between now and Carter's expected summit meeting next month with Soviet President Leonid I. Brezhnev.

It was reported in Moscow yesterday that the summit, at which the treaty is to be signed, will take place June 13-14 in Vienna (story on Page A12). But in Rome, where she was visiting, Rosalynn Carter was quoted by an American Embassy official as telling Italian President Sandro Pertini that the treaty will be signed June 15 at an unspecified European location. An official announcement of the dates for the summit and the side is expected today.

In the weeks between now and the summit, White House officials said yesterday, the administration will be engaged in an intensive public relations campaign designed, in the words of one aide, "to solidify and intensify" widespread public support for arms control in general.

"Our problem is that the intensity of the opposition, although smaller in terms of numbers, is much greater than the support for the treaty," he said.

The administration effort received a boost when Senate Foreign Relations Committee Chairman Frank Church (D-Idaho), in a speech last night, strongly endorsed the SALT II accord and warned against falling into "the trap of technicalities" during the coming debate.

The president, who took no part in the announcement Wednesday that the United States and the Soviet Union had reached basic agreement on a SALT II accord, kicked off the campaign yesterday in an unlikely forum-a breakfast meeting at the White House with members of the American Retial Federation.

Applying a hard-sell technique to the upcoming Senate battle over the pact, Carter warned of dire consequences to the United States and the cause of world peace if the treaty is rejected.

The president called approval of the treaty "the most important single achivement that could possibly take place for our nation during my life-time," and told the retail merchants, with reporters invited to listen:

"Rejection of this treaty, now that it has been negotiated, would be a devastating blow to the United States of America and to the Soviet Union. It would harm our nation's security and it would be a massive, destructive blow to world peace."

Tracing the history of U.S. efforts to restain nuclear arms competition, Carter added, "All of those efforts, which have been shared not only by me but by every president since President Eisenhower, would be endangered if we now reject this treaty. We would be looked upon as a warmonger, not as a peace-loving nation, by many other people of the world."

The president also warned that rejection of the SALT II accord would encourage the spread of nuclear weapons to the developing nations of the world, which, he said, would then have a reason to dismiss U.S. pleas not to develop atomic arsenals.

There and similar arguments will be made repeatedly by Carter and other administration officials in the coming months, leading up to the climactic Senate vote on the treaty, which is not expected until fall at the earliest.

Essentially, the White House plans a two-tiered campaign to gain approval of the treaty. One will be an intensive lobbying effort in the Senate, turning on the hundreds of technical details of the treaty and the administration argument that the terms of the accord protect U.S. national security interests and can be adequately verified.

The other will be a more emotional appeal to the public on the overall issue of "war and peace" in an attempt to create a political atmosphere favorable to a vote for the treaty.

Carter made an indirect reference to this administration strategy in his talk yesterday to the retail group.

"The treaty is very complicated," he said. "Some senators will study every word of it, as I have. Some will listen primarily to the voice of America, as represented by you and those who look to you for leadership."

To begin shaping the "voice of America" the administration hopes the Senate will hear next fall, the White House yesterday dispatched a 10-member State Department team to speak with news organization editorial boards across the country, and mailed written material on the SALT agreement to 6,000 news organizations.

Between now and the summit conference, officials said, about 700 leaders of a broad spectrum of organizations from around the country will be invited to the White House for SALT briefings by the president and others.

White House aides said a decision was made to launch the public relations campaign before the treaty is signed to capitalize on the intense media attention on the issue, which was triggered by Wednesday's announcement and is expected to build to a peak at the Carter-Brezhnez meeting.

There is also a recognition in the White House that the debate is going to be so long and technical that it will be difficult to focus public attention on it, particularly with the normal distractions of the coming summer.

Even before the summit, the president is expected to speak often about the treaty in public appearances in Washington and elsewhere.*