A month-long police investigation has found "insufficient evidence" to charge two Washington Redskins with sexually assaulting a 20-year-old Reston woman last month, Fairfax County's prosecutor said yesterday.

Prosecutor Robert F. Horan Jr. said in a brief press release that he had reached that conclusion after consulting with the county's chief of detectives and investigating officers from the sex crimes division. "It is their conclusion and mine that no criminal charges are warranted in this case," Horan said. "I have no doubt whatsoever that there is insufficient evidence upon which to base a criminal prosecution."

The woman had alleged that she was sexually assaulted by two Redskin players in the Reston apartment of a third team member on Sept. 7, a day before the team's season opener against the Dallas Cowboys. The two Redskins never were identified, but Horan said yesterday that investigators had "extensive interviews" with both.

Horan added that one of the players voluntarily submitted to a three-hour polygraph (lie detector) test. A police official said the investigation apparently became public when Redskin players discussed the probe with reporters Sept. 21 during an airplane flight home following a loss to the Oakland Raiders.

At Redskin Park yesterday, team officials were pleased with the Horan's announcement. Redskins' spokesman Joe Blair said the team was happy that "the charges were found to be completely unfounded.

"We are also pleased that any cloud on the reputation of two very decent men has been completely removed," Blair added.