An Arlington judge cleared Harold C. Lyon, the suspended director of federal programs for gifted and talented children, of a prostitution charge yesterday but ruled there was sufficient evidence against him on another sex charge to merit further court action.

The ruling by General District Court Judge Thomas Monroe means that a grand jury will consider a charge that the 46-year-old Lyon, on leave from the Education Department, engaged in a conspiracy to pander with the wife of a former State Department official.

Lyon, who also is a licensed psychologist and the author of three books that emphasize self-awareness and sexual liberation, was arrested by Arlington police Oct. 14 on various prostitution and pimping charges. He has pleaded innocent to all the charges, which carry a maximum penalty of 30 years in prison, and is free on $5,000 bond.

Detectives testified yesterday that they encountered Lyon, a Middletown, Md., resident, after answering an advertisement he placed in Met Personals, a Washington sex-oriented tabloid, offering the services of a "beautiful, petite . . . young lady" who "models submissively with boyfriend or alone" for "sincere, generous, gentle people."

That turned out to be 27-year-old Susanna McIntyre, who testified yesterday that she gave Lyon 20 percent of the money she made posing for pornographic pictures. In halting English, the Argentine-born McIntyre said she met Lyon three months ago after she placed an ad in the tabloid.

"We had lunch at my house and talked and we had sex and he took some pictures of me," testified McIntyre. During subsequent meeting she said Lyon told her what to charge for her modeling services and how much of a cut he would receive.

McIntyre and her husband Kevin-John McIntyre, who last month resigned his State Department post, were arrested by Arlington police on Oct. 2. Detectives, posing as customers seeking to make a pornographic movie, paid the McIntyres $300 to film them having intercourse. The couple was charged with sodomy and prostitution.

Susanna McIntyre told Judge Monroe yesterday that police promised her that they will drop charges against her if she cooperates and testifies against Lyon. She said she had arranged to meet Lyon in a high-rise apartment being used by police on Oct. 14.

McIntrye avoided looking directly at Lyon during most of the four-hour hearing. A thin, slightly built man clad in a three-piece blue plaid suit, Lyon assiduously scribbled notes during the hearing.

Arlington detective David G. Green said he met Lyon there. "I stated that I had heard of him through Mrs. McIntyre and that he, in fact, was her agent and he said he was . . .

"I said I was there to have sex with Mrs. McIntyre originally . . . and I asked him if he was inclined to join us," said Green. The detective testified that after Lyon agreed to perform oral sex on him he gave Lyon $200 in cash and arrested him on the prostitution charge. Green said that at the time of Lyon's arrest he seized 75 letters to a post office box from people seeking to purchase sexually suggestive films and photographs, sexual paraphernalia Lyon had bought and color snapshots of a woman having sex with a St. Bernard dog.

Lyon's attorney John Karr said his client did nothing wrong. "At stake here is the freedom and reputation of a criminal defendant based entirely on what was organized, orchestrated, produced and directed by members of the law enforcement agency of Arlington, Virginia," he said.

Assistant Commonwealth's Attorney David Cayer defended the police. "The pandering offense involves, the simplest way you can put it, a pimp and a prostitute. In this case Lyon was the pimp, McIntyre the prostitute," said Cayer who told the judge that Lyon "accepted the money for prostitution . . . and was ready and willing to perform that act before Det. Green placed him under arrest."

Monroe said that while there was ample evidence to warrant further action on the conspiracy charge, prosecutors failed to prove Lyon had committed prostitution. "If nobody disrobed, nobody committed adultery, fornication . . . oral sex or sodomy" said Monroe then "even the acceptance of money under the statute" is insufficent evidence to convict.