FBI officials surfaced a Soviet intelligence colonel at an elaborate news conference yesterday to explain how they turned him into a "double agent."

Col. Rudoph Albert Herrmann of the Soviet KGB spoke to reporters from behind a frosted glass screen with his voice altered to protect his new identity.

He described his 11-year-long mission of collecting political intelligence and arranging secret exchanges of information with other Soviet intelligence operatives while he was posing as a free-lance photographer in the surburbs of New York City.

The publicity was designed to show the American public what Soviet intelligence was up to in this country, FBI spokesman said officially in a time reminiscent of the Cold War.

Unofficially, sources said the disclosure also was designed as a slap at the Soviet Union, in the wake of deteriorating relations with the United States since the Soviet invasion of Afghanistan, and to observe how Soviet intelligence would react.

Despite the hoopla of the briefing Herrmann's story was not the staff of James Bond spy novels. It didn't even match the drama of the more modern antihero spy stories of John Le Carre.

Herrmann spent his time, he said, acting as a sort of clandestine political reporters, collecting information from public not classified, sources. He worked dilgently to blend into his Hartsdale, N.Y. neighborhood, spent lots of time preparing his income tax returns even designating $1 a year for the presidential campaign fund.

He set aside time each weekend to listen for coded messages transmitted to him from Moscow. And from time to time he traveled to Fayetteville, Tenn., to Chicago, to El Pasco, to locate or recover information from designated "dead drops."

Herrmann said he once got orders to send an anonymous letter to American space officials saying that an Apollo manned fight was sabotaged. The space agency sent the letter to a "crank-letter" file. The flight went off as scheduled.

Another time he tried to get close to an unnamed presidential candidates, but only bumped into him once accidentially at the San Francisco airport.

For his efforts, he got promoted several times, he said.

Through his experiences didn't sound particularly glamorous, American counterintelligence specialists were pleased about catching and turning Herrmann to their side in a clan-destine battle of wits where victories are difficult to measure.

Homer Boynton, executive assistant director of the FBI, said Herrmann was considered a "big fish" among Soviet intelligence officers who are here illegally -- in contrast to the "legal" spies who operate under diplomatic cover at the Soviet Embassy here or the Mission in New York.

According to the FBI presentation, Herrmann began his career with the KGB while serving in the military in a Soviet-bloc country in Eastern Europe. He was infiltrated to West Germany, than Canada, and finally in 1968 to the United States.

He apparently was identified "a number of years ago" -- the FBI wouldn't be more specific -- when another spy under diplomatic cover was followed to a drop site and Herrmann showed up a short time later.

When confronted by the FBI, he chose to cooperate rather than face prosecution. He was said to be particularly anxious to prevent the KGB from training his teen-age son as a syp too.

Boynton maintained that the value of an agent like Herrmann to the Soviets would be enhanced it intelligence officers with diplomatic cover were forced out of a country.

Boynton said operatives such as Herrmann, when turned around, are useful in confirming knowledge about Soviet techniques, such as the coded letters Herrmann sent to Moscow by way of front addresses in Europe.

One source said later other Soviet intelligence officers left the country hurriedly last year when they became aware that Herrmann had been "doubled" by the FBI.

On Andover Road in Hartsdale, N.Y., the neighbors of the Soviet spy said the family was "friendly" but kept, to themselves." The family moved five months ago, leaving much of its furniture behind. The house is still up for sale, for $85,000.

Neighbors said they had fond memories of the family. Inga Herrmann volunteered to help with therapy treatments for a neighbor boy with cerebral palsy.

Son Michael, 15, mingled freely with the children in the area. He told playmates his father was Czechoslovkian.

Another son, Peter, told neighbors he was a student at Georgetown University.

Family members told others they traveled often during the summer, to their homeland Germany, they said. The FBI said Herrmann periodically traveled to Europe, where he picked up a different set of documents and continued on to Moscow for debriefing and additional training. His most recent trip was in 1977.

Herrmann was known to his neighbors as a free-lance film producer. The family had two cars, a Checker and a Mercedes, though Herrmann said yesterday that his KGB masters gave him little more than expense money for his trips.

The KGB colonel, who said he was about 45, said he never tried to recruit Americans to give him classified military secrets.

Yet he said he felt he had harmed the United States in the days before he went to work with the FBI by transmitting sensitive information collected by other spies and by identifying American citizens about whom Moscow was curious.

Herrmann said he thought he was caught by the FBI because of a mistake by his Soviet handlers and noted that he was appearing in the news conference as part of his "deal" to cooperate with the FBI.

Boynton said Herrmann is the first "illegal" KGB agent to be identified publicly without being prosecuted. The most notorious case of a non-diplomat KGB official involved the exposure of Col. Rudolph Abel in 1957. Like Herrmann, Abel operated out of a photography shop in New York.

Unlike Herrmann, Abel spent his time microfilming U.S. military secrets and was tried and convicted. He later was exchanged for U2 pilot Francis Gary Powers, who was shot down on a flight over the Soviet Union in 1960.

When the Herrmann family left its home in Westchester County five months ago, they told neighbors they were going to Guatemala. Instead, according to the FBI, they will be relocated with a new identity somewhere in the United States.