Former U.S. president Richard M. Nixon and Soviet Central Committee Secretary Anatoliy Dobrynin held two hours of talks in a Moscow restaurant today, Nixon spokesman John Taylor said.

The discussion, which Taylor said was dominated by the subject of U.S.-Soviet affairs, occurred as officials from Washington and Moscow are seeking to define the terms of the second summit meeting between President Reagan and Soviet leader Mikhail Gorbachev.

Nixon spoke with Reagan before leaving for Moscow and is prepared to report back to the president after he returns to the United States this weekend, Taylor said.

Taylor termed Nixon's stay in the Soviet Union "private," and "a fact finding mission," even though the former president met Tuesday with Soviet President Andrei Gromyko, lectured at the Institute for the Study of the U.S.A. and Canada, and met with its director, Georgi Arbatov.

Nixon is staying in the Soviet capital as a guest of the state and his meetings with top Soviet officials have been at Soviet request. It was unclear whether a meeting between Nixon and Gorbachev will take place, but a second Nixon-Dobrynin meeting is tentatively scheduled for Friday.

Both Nixon and Dobrynin forged reputations in Washington as arms control proponents before 1974, when the Watergate scandal forced Nixon to resign. Dobrynin was serving as Soviet ambassador to the United States at the time.

In March Dobrynin became a Central Committee secretary and one of Gorbachev's key foreign policy advisers.

Nixon comes to Moscow with more experience in U.S.-Soviet summitry than any living former president. The only U.S. president to visit Moscow, he held meetings here in 1972 and 1974 with then-Soviet leader Leonid Brezhnev.