The United States and Soviet Union moved closer in recent weeks to establishing special centers for superpower cooperation to reduce the risks of an accidental nuclear war, according to two senators who took the idea to the White House and the Kremlin.

Sens. Sam Nunn (D-Ga.) and John W. Warner (R-Va.) said in interviews that the Reagan administration, after five months of interagency deliberation, gave its endorsement Aug. 26 to a scaled-down version of "nuclear risk reduction centers" in the two capitals.

Nunn and Warner then took the administration-backed proposal, plus their own suggestions about later expansion, to Soviet leader Mikhail Gorbachev in a Kremlin meeting Sept. 3.

Gorbachev was "very positive" in his comments about the proposal, the senators said. Nunn added that the Soviet leader said the plan deserves attention and that Gorbachev would see that it receives it.

The next step, Warner said, could be discussion of the possibilities by the two nations in the Geneva arms control talks, in the Nov. 19-20 summit meeting of President Reagan and Gorbachev, or through another diplomatic channel.

The original version of the Nunn-Warner plan, as presented by them to a meeting of officials of executive branch agencies March 22, called for the centers to be used in part for U.S.-Soviet discussions and information exchanges about possible use of nuclear weapons by "unauthorized parties" -- a euphemism for terrorists.

That feature of the plan was not endorsed by the Reagan administration in the Aug. 26 classified letter from White House national security affairs adviser Robert C. McFarlane, according to the senators. One source said there were worries in the administration about discussing with the Soviets contingency plans for dealing with international terrorism.

In their presentation to Gorbachev, the senators listed the talks about "unauthorized" nuclear threats as "roles that might be added in the future" to the proposed centers rather than roles proposed for their initial operation.

In the same category of possible future moves was the idea of joint U.S.-Soviet manning of each center. Though the senators were interested in exploring joint manning, administration officials objected that this could present "an intelligence hazard" and a "disinformation opportunity."

As endorsed by the administration and presented to Gorbachev, each center initially would be manned exclusively by diplomats and military personnel of its host country, although "designated liaison officers" from the other side's embassy would have periodic access to the center "under controlled escort."

The centers, in this initial phase, would "maintain a 24-hour watch on any events with the potential to lead to nuclear incidents." The equipment would include up-to-date communications gear, equivalent to that approved by the two nations last year for the "upgraded hot line" between Moscow and Washington.

The U.S. administration agreed that the nuclear risk reduction centers, which are to be established separately from command headquarters where the hot line is based, would be a meeting place for U.S.-Soviet discussions about nuclear risks and a site for "high-level military exchanges." Among other things, the senators said, the discussions should "promote a dialogue on nuclear doctrines, forces and activities."

"This is not intended to be a substitute for the hot line, something that deals with a crisis when it occurs, but an attempt to get out in front and head off a crisis before it happens," Nunn said.

Nunn said that, despite doubts in some quarters of the administration, reportedly including the Pentagon, he thinks the centers are in the U.S. national interest. "If you avoid one problem between the United States and Soviet Union every 30 years," he said, "it would be well worthwhile."

The centers, which were not accepted previously by the administration, were recommended by the Senate early last year in an amendment sponsored by Nunn and Warner.