The Reagan administration said yesterday it stands by its contention that the Soviet bloc has used chemical weapons in Asia.

The Washington Post reported Sunday that while the State Department was actively pursuing the charges, the government was accumulating and withholding evidence that suggested they weren't true. An account in Foreign Policy magazine, released Sunday, said government researchers who visited Southeast Asia starting at the end of 1983 concluded that the administration erred when it made its initial allegations two years earlier.

In 1981, then-Secretary of State Alexander M. Haig Jr. accused the Soviets and their allies of using a lethal substance, known as "yellow rain," in Cambodia and Laos in violation of international agreements. The targets supposedly were rebel groups and refugees.

State Department deputy spokeswoman Phyllis Oakley said yesterday the administration "has no reason to change its earlier conclusions."

Oakley said that by the time the administration publicly addressed the issue in 1981, it had been under intense U.S. government study for five years. She acknowledged that reports of chemical warfare use in Asia have subsided in recent years.

White House spokesman Marlin Fitzwater, asked about the reports in Santa Barbara, Calif., said, "We don't have any reason to question the original conclusion of those studies. The studies have not changed. We don't know of any new information."

The Foreign Policy article is entitled "Yellow Rain: The Story Collapses."