Soviet leader Mikhail Gorbachev said today that the Soviet Union would seek a nuclear test ban agreement that included "an appropriate system of verification measures -- both national and international ones."

Answering questions put by the Soviet news agency Tass one week after Moscow imposed a five-month moratorium on its nuclear testing program, Gorbachev said unilateral steps alone would not stop nuclear tests.

"An international agreement is essential for the problem to be solved once and for all," he said.

Gorbachev's comments were seen as a response to Washington's emphasis on the importance of verification of any agreed halt in nuclear testing. Washington has rejected the Soviet moratorium, offering instead to allow Soviet observers at underground nuclear testing sites.

But Gorbachev insisted that a moratorium should come before on-site verification. He also noted that technology already exists to detect a nuclear explosion "even of a small yield."

Washington dismissed the Soviet proposal the day it was offered and said it wanted to ensure that a ban on testing was verifiable before joining the Soviet moratorium.

Reagan administration officials also said that the Soviets had conducted three nuclear tests last week just before issuing the moratorium proposal. Senior administration officials said the Soviets had been speeding up their testing program so that further testing would not be required this year.

Gorbachev rebutted those assertions today, saying that Moscow left its nuclear testing program "unfinished" when it went ahead with a unilateral moratorium on Aug. 6.

The Soviet decision to begin a five-month suspension of nuclear testing on the anniversary of the Hiroshima bomb was made after "a thorough and comprehensive study," Gorbachev said. "It was not an easy matter at all to take such a step."

Gorbachev said that the Soviet Union had conducted as many nuclear tests as the United States this year and that overall, U.S. nuclear tests to date outnumber Soviet ones. "And they in the White House know it," he added.

Gorbachev called for a resumption of talks on nuclear weapons testing among Britain, the United States and the Soviet Union. He said the Soviets also were willing to discuss the issue at the Geneva conference on disarmament.