A well-placed Soviet aviation and electronics expert arrested by Soviet security agents in June for passing secrets to the Central Intelligence Agency was exposed by former CIA officer Edward L. Howard, who eluded capture in New Mexico last month, according to intelligence community sources.

Howard, fired by the CIA in June 1983, allegedly began selling secrets to Soviet intelligence last October. He fled his home outside Santa Fe Sept. 21 while under surveillance by FBI agents and is presumed to be in the Soviet Union, authorities said.

The Soviet expert, A.G. Tolkachev, was first identified as a U.S. spy in reports by the Soviet news agency Tass Sept. 20.

In The Wall Street Journal yesterday, editorial writer William Kucewicz reported, "Tolkachev was one of the CIA's most valuable human assets in the Soviet Union. And his exposure by Howard and arrest stand as indictments of gross mismanagement and ineptitude reaching to the highest levels of U.S. counterintelligence operations."

The CIA had no official comment on the Journal report, but several intelligence community sources indicated that information fed by Howard to Soviet intelligence officials over the last year led to exposure of Tolkachev.

The Soviet was described as a research institute expert in new aircraft technology, including advanced avionics, electronic countermeasures, radar and "stealth" technologies to conceal aircraft and cruise missiles.

" Tolkachev saved us billions of dollars in development costs," The Journal quoted a "well-placed source" as saying.

Intelligence officials also confirmed that Howard acknowledged drug use when hired by the agency in 1981, and they said he was fired after acknowledging in a 1983 polygraph examination that he had failed to stop using drugs.

One CIA official said hiring Howard despite acknowledged drug use should not be considered surprising in a social setting that included easy access to recreational drugs, and the official stressed that Howard pledged to end drug use after joining the agency.

After that pledge, Howard then entered a training program to become a CIA case officer in the U.S. Embassy in Moscow. The Journal said Howard was taught how to supervise Tolkachev as an agent, which would have involved collecting information clandestinely from Tolkachev's work on Soviet aviation projects.

Tass reported that KGB officials who searched Tolkachev's apartment in June found "miniature cameras of a special design by means of which he Tolkachev photographed secret documents" along with "codes and ciphers, quick-acting two-way communications radio apparatus and other equipment for espionage work."

At the time of Tolkachev's arrest, the Soviets also expelled Paul M. Stombaugh, a U.S. Embassy political officer, alleging that he was a CIA officer caught in the act of receiving secrets "of a defense nature" from Tolkachev.