President Carter and Soviet President Leonid Brezhnev ended their first summit today by signing a new strategic arms limitation agreement and pledging to move "as soon as possible" into the next phase of SALT negotiations.

The muted celebration in the gilded Redoutensaal of the imperial Hofburg palace, where the two leaders exchanged signatures and diplomatic kisses, suggested that the summit fulfilled no more than the modest expectation U.S. officials had anticipated.

A joint communique issued at the end of three days of talks showed no agreement about regional disputes in Africa, Asia and the Middle East and included only vague statements about the need to reduce troop levels in Europe and the resolve to proceed with other arms control negotiations.

The treaty, Carter said after signing the leather-bound document, places "important new limits on both the number and quality of nuclear arms, and it allows us to continue on course toward a safer world with even more substantial limitations and reductions in SALT III.

"We cannot interrupt or endanger this process."

The 72-year-old Soviet leader in his remarks said the treaty underscored a joint desire "to act in such a way as to prevent an outbreak of nuclear war."

"In signing this treaty we are helping to defend the most sacred right of every man - the right to live," Brezhnev said.

Apart from the already publicized aspect of the complex treaty, the only outstanding issue-involving the Soviet Backfire bomber-was resolved by the two leaders after a heated exchange during their meeting yesterday morning, according to U.S. officials.

On Saturday, Brezhnev handed Carter a statement asserting that the Soviet Union did not intend to give the Backfire "intercontinental" capability either by increasing its radius or through in-flight refueling. But the Soviets would not state the rate of their current production, although Brezhnev's statement said it would not be increased.

White House press secretary Jody Powell said that the plan was for the United States to state during Saturday's meeting that the production rate was 30 Backfires per year and the Soviets were to agree to this figure. But an examination of the record Saturday night disclosed to U.S. officials that the Soviet assurances were "not sufficient," Powell said.

As a result, Carter raised the issue yesterday morning, telling Brezhnev that failure to confirm the production rate would be a breach of "good faith" under which they have come to Vienna to conclude the SALT II.

In an atmosphere of tension and heated arguments that reportedly included a last-minute Soviet threat to bring U.S. forward bases in Europe under SALT, Brezhnev finally threw his hands into the air and said "the production will not exceed 30," according to an American participant.

Brezhnev was reported as saying at that point that he was making another "Soviet concession."

Carter and Brezhnev began their last day at the Vienna summit with a private meeting at the U.S. Embassy. The session, which lasted for an hour and a half, was the first time that the two leaders had been together alone, with just their interpreters present.

Press secretary Powell said that Carter told him that he and Brezhnev had agreed in this session to increase the frequency of their meetings and that the two leaders had exchanged invitations to visit their respective countries.

Carter specifically noted, according to Powell, that the two presidents agreed that they will not wait for a crisis or an event such as a treaty signing to have their next meeting. Carter had wanted to meet with Brezhnev early in his presidency, but the Soviet leader had made it clear that he did not want to meet until they had a SALT II treaty completed. Carter also said, according to Powell, that there was "substantial conformity" in the general views of the two presidents toward the reduction of arms under SALT III.

Following their morning meeting, Carter and Brezhnev traveled across Vienna to the Soviet Embassy, where they held one last meeting along with their full delegations of advisers. They met for just 35 minutes.

Most of the time was taken up with Brezhnev discussing bilateral U.S.-Soviet issues. Carter said that because of the press of time, he would forego his own statement on the bilateral issues, and would instead study Brezhnev's statement.

This enabled the two presidents to adjourn and get to the signing ceremony on time-1 p.m. Vienna time-and the ceremonies were thus duly televised live back to audiences in Washington and Moscow on schedule.

Except for the backfire controversy, the summit ended on a positive note, although a joint communique indicated that no program was made on arms control matters other than SALT II.

After more than six years of negotiations, the SALT signing today was an accomplishment for both sides. After putting their names to the document, Brezhnev and Carter rose and shook hands as the audience of American and Soviet officials and guests applauded. Then Carter leaned his head toward Brezhnev's as he grasped the Soviet leader's shoulder and the two presidents kissed first on the left cheek then on the right.

Most of the numbers in the treaty and the accompanying protocol, joint statement of principles, and side memorandums had already been known well before the summit convened.

In the signing ceremonies, both presidents spoke of the need to continue negotiations beyond SALT II in an effort to reach future agreements that will significantly reduce the stockpiles of existing nuclear weapons.

Brenzhnev, who spoke first, said "the entry into force of this treaty opens up the possibility to begin elaborating subsequent measures to not only limit but also reduce strategic arms."

Carter at one point couched his message of peace in pugilistic terms.

"In the end," Carter said, "peace can be won only if we have pursued it and struggled tenaciously to keep the peace all along. Yet this fight for peace has often seemed the most difficult to win.

"Here today, as we set careful limits on our power, we draw boundaries around our fears of one another. As we begin to control our fears, we can better insure our future."

In their meetings, the two presidents touched on a number of issues of global differences between the United States and the Soviet Union. According to briefings by American officials, there were frank exchanges of views that did much to clarify the conflicting positions but did little to resolve them.

Carter reiterated the American displeasure at the actions of Cubans in Africa and Vietnamese in Cambodia, both of which are supported by the Soviets. Brezhnev voiced his displeasure at the separate Egyptian-Israeli peace treaty and said he would not support any United Nations effort to oversee the situation in the Sinai peninsula.

The two sides discussed mutual balanced force reductions in Europe.

They made no concrete progress, U.S. officials said, but the Americans did come away feeling that perhaps the Soviets are more anxious to actually reduce force levels than they have been in the past.

Carter discussed human rights in his private meeting with Brezhnev this morning, but U.S. officials could not provide any details of just what was said.

Nor could they say immediately whether Carter had raised the issue of Soviet assurances on emigration of Jews in exchange for granting Moscow most-favored-nation trade status. Such assurances are required by the Jackson-Vanik amendment.

American officials conceded that most of the discussions of divisive issues did not produce significant breakthroughs-and this, they note, is precisely what they had been telling reporters to anticipate.

American officials give great significance to Carter's presentation on SALT III, given the new generation of weaponry of the 1980s. They liken Carter's presentation to the first U.S. mention of strategic arms limitation at the 1967 Glassboro summit. They hope this will be viewed as an accomplishment even though, like Glassboro, there is not much of visible importance that was decided in Vienna. A total of 16 signatures were required by each president for the English and Russian language copies of the SALT II documents. At the table, they actually signed only four times, with the other documents having been done in advance of the ceremony.

The treaty will be in effect until 1985 if it is ratified by the U.S. Senate-a prospect that is at present far from certain.

It sets an initial limit for all types of missile launchers-whether based on land, sea or airborne bombers-at 2,400. This initial ceiling will then be reduced to 2,250 launchers by the end of 1981. Since the Soviet now have 2,520 delivery vehicles, this means they will have to dismantle 270 of their present number by 1981. The United States, since it now has only 2,058, will be able to add to its total in order to reach the maximum number allowed.

Of the total of 2,250 launchers allowed, neither side can have more than a total of 1,320 that are equipped with MIRVs (multiple, independently targeted warheads that fit on a single missile launcher) or with cruise missiles (in the case of bombers).

The number of MIRVed warheads allowed on any missile will be frozen at the number that each side has tested on each type of missile. Thus the Soviets would be permitted 10 warheads on each of their heavy missiles, American officials said.

In a key provision, "encryption" (or coding) of "telemetry" (radio signals from test rockets) is banned specifically in an understanding attached to the treaty.

The protocol to the treaty will expire at the end of 1981. It bans the deployment of mobile missiles but it does not prohibit the development to mobile missiles and Carter has already announced that the United States intends to go ahead with its development of the mobile MX. CAPTION: Picture 1;, Brezhnev kisses Carter's cheek after the two presidents signed the second strategic arms limitation treaty in Vienna. UPI; Picture 2, Watching President Carter and Soviet leader Leonid Brezhnev sign the strategic arms limitation treaty in Vienna are, from left: national security adviser Zbigniew Brzezinski, Defense Secretary Harold Brown, Secretary of State Cyrus Vance, Soviet Foreign Minister Andrei Gromyko, Ambassador Anatoliy Dobrynin and Defense Minister Dmitri Ustinov. AP