When undercover D.C. police officers recently walked into a Southeast Washington building where they suspected illegal alcoholic beverages and sex were being sold, they came across one of their own.

"You're not going to raid this place, are you?" off-duty Officer Stanley B. Roberts reportedly asked one of the plainclothes detectives. "No," answered the detective.

However, minutes later, uniformed officers joined the undercover detectives in announcing a raid of the building at 36 N St. and arrested 10 persons present, including Roberts.

Roberts and six others were charged with sodomy and the remaining three were charged with selling alcoholic beverages without a license.

The arrests stemmed from a six-week undercover investigation of the two-story brick structure. In the raid last Friday, police confiscated several gallon-size bottles of wine, a foam rubber matress and sheet, pornographic slides and films, a slide projector, a film projector, a cloth screen, stereo equipment, 28 assorted bath robes, numerous business cards and a mailing list.

According to an affidavit filed with the search warrant for the building, police were informed of the alleged activities there by a citizen who wrote a letter to Police Chief Burtell M. Jefferson. The affidavit did not name the citizen. The citizen also gave police a telephone number she had heard on a local radio station, the affidavit stated.

Officer S. H. Bennett called the number and got a recorded message stating, among other things, "that parties would be held Tuesday through Sunday" at the 36 N St. SE address and he should call another number for further information, the affidavit said.

When Bennett called that number, a female answered according to the affidavit. Bennett told the woman he had an out-of-town friend who had heard about the club and asked whether he had to be a club member to be admitted with his friend, the affidavit said. He was told he did not, according to the affidavit.

Bennett then asked the cost and was told $10 per couple before 10 p.m., and $25 per couple after 10 p.m., according to the affidavit.

On January 9, Bennett and three other undercover police officers, including two women, went to the club, the affidavit said. They were led to a room where they took off their clothes, except for underwear, and put on robes, according to the affidavit.

They were then led to the second floor, where soft-core pornographic pictures were being shown on a large screen on the wall, the affidavit said. About 20 people were present, and "several persons were engaged in sexual relations, including but not limited to group sex and sodomy," the affidavit stated.

After Jan. 9, police kept the building under surveillance. Several couples and unattached people were seen entering the building, the affidavit said.

Police raided the building at 11:45 p.m. last Friday. In addition to Officer Roberts, arrested on sodomy charges were Michael J. Fuschs, 37, of 5819 Fisher Rd., Temple Hills; Steve L. Einbinder, 30, of 825 New Hampshire Ave. NW; Robert Neishieb, 39, and Dorothy Neishieb, 31, of Salem, Ohio; Harold R. Witmyer, 60, of 6766 Woodley Rd., Baltimore, and Sharon Edwards, 25, of 1414 Corcoran St. NW, police said.

Charged with selling alcoholic beverages without a license were Dennis Solbin, 37, of the 36 N St. address; Michael Totten, 34, of 6210 Addison Rd., Seat Pleasant; and Sylvia Vacchio, 31, of 8105 New Hampshire Ave., Hyattsville, police said.

Roberts, a 10-year police veteran assigned to the helicopter branch, has been placed on administrative leave with pay pending an investigation.He could not be reached for comment.