Svetlana Ogorodnikova is so unprepossessing in personality and appearance that she seems incapable of being the center of such confusion and melodrama.

Last June, the Soviet emigre, 35, and her husband Nikolai, 53, pleaded guilty to conspiring to commit espionage. Their surprise admission came about halfway through the first trial of an FBI agent for espionage, one marked by Ogorodnikova's emotional outbursts.

She later managed to bring agent Richard W. Miller's second trial to an abrupt, if temporary, halt. By his account and hers, Miller is her former lover.

Fired minutes before his arrest in October 1984, Miller is being retried on charges that he gave Ogorodnikova classified documents in return for her promise of $65,000 in cash and gold. The first trial ended last November with a dead-locked jury.

Miller's lawyers rested their case last week after 24 days of defense testimony. More than half of those days were devoted to testimony of Ogorodnikova, who had not testified in Miller's first trial or her own.

Three days after she took the witness stand, U.S. District Court Judge David V. Kenyon stopped the proceedings and sent the jury home, saying an "important new development" had to be resolved.

When court resumed the next day, it was revealed that Ogorodnikova had gone to the judge's chambers and recanted her guilty plea. "Richard is not a traitor . . . I am not a Russian spy," she told Kenyon in an emotional assertion of innocence.

The judge released a transcript of the session.

She said she had agreed to accept a plea bargain at her trial last year to avoid a life sentence. "They told me I was Russian . . . that nobody maybe would believe me," she said. It was not clear who she meant by "they."

She told the judge that she was moved to tell "the truth" when she saw Miller's son, 17, among courtroom spectators on the first day of her testimony at her trial.

Kenyon, who had sentenced Ogorodnikova to 18 years in prison, stopped the proceedings and, after long conferences in chambers, said attorneys who had negotiated Ogorodnikova's plea had no conflict of interest in continuing to represent her.

Testifying at the current trial, Ogorodnikova appeared almost totally different than when she left the same courtroom less than a year earlier to begin serving her sentence.

Her hair, formerly unbrushed and below her shoulders, was cut, curled and neatly brushed; her ill-fitting clothes were replaced by a neatly tailored tan pants outfit with epaulets. She wore a touch of make-up.

Her attorneys say she has an IQ of 74. She testified that she was drunk virtually every day for two years.

"I started to drink," Ogorodnikova testified, "from the moment when I broke up with" former FBI agent John Hunt. "I wanted to forget everything."

Hunt, who retired soon after Miller and the Ogorodnikovs were arrested, has testified that he tried to recruit Ogorodnikova as an informant but was never sexually involved with her. She said that they began a love affair in 1982 and that he said he would leave his wife and marry her.

Last year, in her trial, Ogorodnikova wept during Hunt's testimony and shouted at him, "Why you lie?" In testimony, she described Hunt as "a liar." The FBI, she said, had driven her "crazy."

In her 13 days of testimony, Ogorodnikova seemed to ricochet through an emotional gamut: nervous, then weary and dispirited, suddenly irritated, often weepy and contradictory.

She told the judge that she had changed her story because of Miller's son; she tearfully told the jury that she was motivated by her love affair with the defendant.

Miller's attorneys asked for a mistrial because they were unaware when they subpoenaed her that she would admit, under cross-examination, to having directed her attorneys to tell Kenyon that she had received classified documents from Miller.

Her attorneys have used the defense tactic the used in the first trial, portraying Miller as a bumbler who hoped that he could infiltrate the KGB, the Soviet intelligence service, through Ogorodnikova and resurrect his tattered career.

Much of the testimony from his former FBI colleagues has supported the image of Miller as an inept agent with bad judgment.

Ogorodnikova testified that Miller never passed her classified documents, that she had been trying to help the FBI, that he had been trying to help his FBI career. He was, she said, playing "a political game" to make the Soviets think he was working for them.

When Assistant U.S. Attorney Russell Hayman pressed, "Didn't you ask Mr. Miller to work for the KGB?" she retorted irritably: "Miller knew I was working for the FBI, so how could I ask him to work for the KGB?" But several Soviet emigres have testified that Ogorodnikova was well known in their community for pro-Soviet activities.

Ogorodnikova testified that she had lied previously to her attorneys, the FBI and prosecutors. On her last day of testimony, she said she had lied to Kenyon when she pleaded guilty, and she added, "I'm telling the truth now." She turned tearfully to him and said, "I feel very bad. I please ask for forgiveness."

Testifying last summer at her trial, Miller claimed that she had tried to recruit him, telling him that she was "a KGB major" and offering "a lot of money." Miller's jurors, however, are unlikely to hear about that testimony, given under a use-immunity grant, and must weigh Ogorodnikova's credibility without it.