The United States plans to discuss with the Soviet Union in "late summer or early fall" mutual restraints in selling weapons to other countries, Leslie Gelb, director of the State Department's Bureau of Political and Military Affairs, said yesterday.

Gelb and other government officials spoke to about 250 defense industry executives at a symposium on U.S. arms sales policy.

The meeting, held at the State Department and sponsored by the Electronic Industries Assn., was closed to the press and the public.

Representatives of the Electronic Industries Assn. said, after asking a reporter to leave the session, that government executives had been promised their remarks would be "off the record."

"We are walking a tightrope between our desire for restraint and our desire for national security interests," said Gelb in explaining President Carter's plan for reducing arms exports.

A key to restricting arms sales worldwide is reaching an agreement with the Soviet Union to exercise restraint along with the United States.

Although Carter has said he has received encouraging signs from Soviet leaders in this regard, it was not known until Gelb spoke yesterday that the formal attempt will be made, by this fall.

Current U.S. government restrictions on arms exports are already be ing protested by American defense firms, with Latin America the main source of complaint.

Defense industry representatives complained to government executives at yesterday's symposium that U.S. restrictions on sales to Latin America have left the door open to foreign arms makers.

One contractor representative complained that even commercial helicopters are being denied export licenses for Latin America if they have limited armament aboard.

Gelb, Lt. Gen Howard Fish, the Pentagon's manager of arms exports, and other government officials, said that the United States does not use arms exports to bring in foreign income. Sales are approved, they said, only when U.S. security and foreign policy interests will be advanced.

Another source of industry concern, as evidenced by several questions on the subject yesterday is Carter's desire to discourage the design and development of U.S. weapons specifically for foreign nations.

Fish said there is no intention to deny allies the right to produce American weapons but that supplying them with weapons not in the U.S. inventory is another matter.

He warned against what he called "the losing prototype syndrome," meaning a contractor who loses a Pentagon competition and then tries to sell the design abroad.

William Robinson, director of State's Office of Munitions Control, warned the contractors that "third country sales outside NATO are going to be a distinct exception when they're approved."