The government has hard information that the Soviet intelligence agency, the KGB, sent forged racist letters in the name of the Ku Klux Klan threatening Olympic athletes from 20 Asian and African nations, Attorney General William French Smith and FBI Director William H. Webster said today.

The Soviets acted in an effort to gain support from non-Communist bloc countries for their boycott of the Olympics, Smith said, but "fortunately, none of the nations that received these letters succumbed to the attempted intimidation." He made the statement in a speech to a thousand members of the American Bar Association about the communists' "threat to the international rule of law."

Lawyers and judges from about 30 foreign nations, including African and Asian nations, were in the audience as Smith spoke to the ABA's convention. Webster, who is also attending the meeting, confirmed Smith's comments afterwards in an interview.

Reports of the letters surfaced in early July. They were reportedly mailed from U.S. locations, including Prince George's County and northern Virginia, and threatened violence to athletes. At the time, the Soviet Embassy in Washington and KKK leaders denied involvement.

Smith said today that the letters were "openly racist and disgusting," adding that "a thorough analysis -- including linguistic and forensic techniques" -- had revealed the source of the letters as the KGB.

Neither Smith nor Webster would say more about evidence of KGB involvement, saying they did not want to compromise sources or help the Soviets improve their forgery techniques.

"We're entirely satisfied" that the KGB is responsible for the letters, Webster said.

Asked if the government was basing its conclusion on hard evidence, rather than inference, Webster said "that's right."

Last month, the State Department released a copy of a letter that had been sent to the Olympic committees of various African and Asian countries -- Malaysia, Zimbabwe, Sri Lanka and South Korea -- in the name of the Klan with a postmark of Prince George's County. It was headlined, "Olympic Games for Humans, Not Apes."

The letters, Smith said in his speech, "were not produced or sent by the Ku Klux Klan. They were instead manufactured and mailed by another organization devoted to terror: the KGB.

"Although I cannot detail all of what we know about these documents for fear of helping the authors to refine their efforts, a thorough analysis -- including linguistic and forensic techniques -- reveals that they are classic examples of a Soviet forgery or disinformation operation," Smith said.

"They were intended to aid the Soviets in justifying their boycott of the Olympics and to gain the support of non-Communist bloc countries. Through this plot, the Soviet Union, employing cynical falsehood, struck at both the Olympic ideal and the rule of law.

"It is not, however, unique," he said. "The plot is an example of what the intelligence community refers to as an 'active measure.' By an active measure, the Soviets mean an operation intended to influence or affect another country's policies."

Smith said, "These forgeries are deserving of worldwide censure and should serve as a warning of Soviet efforts."

Smith also reported to the ABA what he said were efforts by Cuba and Bulgaria to use drug-trafficking to finance terrorism and by Nicaragua to use drug sales to finance "revolutionary efforts."

He said three recent federal indictments supported this conclusion. "Just last week, a federal grand jury in Miami indicted 11 persons on drug-trafficking and conspiracy charges involving a major cocaine shipment smuggled into this country via Nicaragua," he said. "One of those defendants -- Frederico Vaughan -- has been identified in court documents as an aide to the Sandinista minister of the interior."

"Any coming together of terrorist or insurgent groups and drug-trafficking must be viewed as an extremely serious threat to law and society," Smith said.

Tuesday the ABA is to consider a resolution criticizing the United States for refusing the International Court of Justice's jurisdiction over covert U.S. activities against Nicaragua.

A second critical resolution, attacking denials of visas to politically objectionable foreign speakers, also will be before the association's House of Delegates. That resolution is expected to be deferred for further study.