Three students surprised a group of alleged bicycle thieves in front of Dunster House Tuesday night and subdued one suspect, who was later released by the Harvard police when the students declined to file a complaint against the suspect.

The group, which appeared to be well-organized and experienced, had a van for loading the bicycles, Michael A. Fitts '75, one of the three undergraduates, said yesterday.

Robert Tonis, chief of Harvard police, said yesterday that no Harvard policeman could legally arrest the suspect unless the officer had actually witnessed the crime.

Tonis said that because the students decided not to file a complaint against the suspect with the Cambridge police, the University police could not detain the alleged thief. He added that if the students had filed a complaint, they could have been sued for false arrest.

Two of the students noticed a youth clipping a bicycle lock and then wheeling a bicycle away at 11:30 p.m. Tuesday, Fitts said. He added that when the youth was asked what he was doing, he replied, "What do you think?"

The youth then handed a large pair of clippers to a companion, who bent down over a second bicycle, Fitts said.

Two students then subdued the second youth, while a third drove away in a van, and the first cycled away, Fitts said.

A Harvard police spokesman said yesterday that since the three students had no actual evidence that the youth had attempted a theft, there was no action that could be taken against them.

"I don't doubt that he was one of them," the spokesman said, "but what could we have charged him with?"