Joseph Mapes, 36, suspected by the Loudoun County Sheriff's Office of stealing a set of Georgia O'Keeffe lithographs from the home of James Stieglitz earlier this month, was in Long Island's Suffolk County Jail yesterday -- waiting to find out if he would be released for lack of evidence.

The problem in a nutshell is this: What Mapes allegedly took is allegedly bogus.

On April 13, Stieglitz -- the 34-year-old grandnephew of Georgia O'Keeffe -- told a Loudoun County investigator that a set of lithographs signed by O'Keeffe had been stolen from his home, allegedly by an interior decorator named Joseph Mapes -- he of addresses in New York and Connecticut. Stieglitz then took an ad in last Thursday's Loudoun Times Mirror to offer a $5,000 reward in hopes of getting the lithographs back.

What neither Stieglitz nor Mapes apparently knew was that the FBI was investigating Stieglitz for allegedly making available for sale fraudulent O'Keeffe lithographs -- which O'Keeffee says she has neither authorized nor signed. On Monday, a U.S. magistrate issued an arrest warrant for Stieglitz, who is still at large.

Mapes has not been so lucky. When he was stopped for a routine traffic check in Sag Harbor, N.Y., Monday, Officer John McMahon discovered that Loudoun County had issued arrest warrants for the interior decorator. So now Mapes sits in the interior of Suffolk County Jail . . . waiting to find out whether the validity of the lithographs will have an effect on the warrants.

The Loudoun County Sheriff's Office was ready to head up to Long Island yesterday to pick up Mapes, until a story in yesterday's Washington Post revealed that the FBI was questioning the validity of the lithographs.

Tom Wiseman of the FBI's Alexandria office said last evening that Stieglitz will "probably surrender himself late today or tomorrow."

Stay tuned. . .