The United States and the Soviet Union will begin talks next month banning hunter-killer satellites in space, Secretary of State Cyrus R. Vance said yesterday.

Vance confirmed in a speech before the American Society of Newspaper Editors that the Soviet Union, as previously reported, has agreed to the U.S. proposal. The objective, he said, will be "suspending antisatellite testing and keeping space open for free and peaceful use by all."

"Evidence that the Soviet Union is developing an antisatellite capability is disturbing," Vance said.

Although the United States is prepared to protect itself 'against such a threat," he said, it is much preferable to prevent an antisatellite race.

Vance also announced that the Soviet Union has agreed to proceed with talks on restraining the sale of conventional weapons. Exploratory discussions about the possibility of limiting arms sales were hald in December.

In reviewing the state of American-Soviet arms control prior to his departure tomorrow for a trip which will take him to Africa and to the Soviet Union, Vance cautioned against exaggerated expectation about what arms control can achieve.

A year ago, Vance's first mission to Moscow brought the administration into head-on collision with the Soviet Union over U.S. proposals for "deep cuts" in strategic arms levels. This time, Soviet President lenoid Brexhnev has charged the administration with displaying "indecision and inconsistency" in the strategic arms limitation talks (SALT).

Vance said yesterday that "if we judge arms control measures against unrealistic standards, we may lose the possibility of making any practical progress."

No arms control agreement, he said, will eliminate all the challenges that confront allied forces, or "dramatically reduce our defense budget," or "guarantee stability in the U.S. Soviet relationship." But they can, he said, "contribute significantly to reducing the prosepect of war."

"We have made substantial progress over the past year" toward a new SALT agreement, Vance said, but "important differences still remain."

"I do not expect to wrap up a SALT agreement" Vance said, but "important differences still remain."

"I do not expect to wrap up a SALT agreement" in the Moscow talks later this month, Vance said in response to a question, but he said he anticipates progress in narrowing differences.

Avoiding setting any time limits on agreement, Vance said the administration is ready to negotiate "as long as it takes to achieve a SALT agreement which enhances our security and that of our allies."

Vance reiterated that he will attempt "no linkage between the negotiation of a SALT agreement and the activities of the Soviet Union in Africa." He said, however, that he expects some discussion about the "large number of Cuba and Soviet forces" in the Horn of Africa.