A former member of the U.S. Army's elite presidential guard, who was convicted yesterday of beating a black off-duty D.C. policeofficer, testified at his trial that he is a member of the American Nazi party.

Frederick T. Verduin, a member of the 3rd United States Infantry at Ft. Myer in Arlington, was a member of the honor guard until about eight months ago when Army officials discovered Verduin was a member of the National Socialist White Peoples Party, formerly known as the American Nazi party.

Verduin was demoted from the 130-member guard, which performs at parades and ceremonies, such as at White House functions, at the Tomb of the Unknown Soldier and at Arlington National Cemetery funerals.

"It is an embarrassing thing as far as the Army is concerned," an Army spokesman said. The spokesman said he didn't know of any other Nazis in the Army and that Verduin's party membership "has not interfered with his military duties." He now is an historian at the Ft. Myer museum.

It is not against Army regulations to be a Nazi as long as the organization is not attempting to violently overthrow the government, the spokesman said.

It could not be immediately determined yesterday whether Verduin was ever at White House ceremonies, but the spokesman said that once it was discovered Verduin was a Nazi, his White House clearance as a member of the honor guard was taken away.

Servicemen may wear other uniforms, the spokesman said, as long as it is not during on duty hours. Verduin testified yesterday that when the assault incident occurred on Set. 3 he was wearing black boots, black trousers, a beige poplin military-style shirt and a red armband with a swastika.

Verduin, a member of the honor guard for about 10 months, testified yesterday in Arlington General District Court that he had just returned from a Nazi rally and convention in the District of Columbia when he stopped at the Redhead gasoline station at 2520 Wilson Blvd in Arlington, to buy a soda.

Off-duty D.C. police detective Edward L. Threat and his wife Karen, who is white, had just returned from buying furniture when they and their two children drove into the Redhead station for gas, the Threats testified.

The detective, who has worked two years as a detective with the 2nd district theft squad, began pumping gas for his car.

Both Threats said a brown Chevrolet Caprice with two men in it wearing Nazi uniforms pulled up next to their car.

The driver of the Nazis' car got out and bought a soda from the vending machine, Mrs. Threat testified, "and gave it to a passenger in the car.

Mrs. Threat said she then went to the machine to get a soda for their children and as she passed the Nazis' car one of the occupants said to her: "More power to the white people, you nigger-loving bitch." On her way back to the car with the soda, the man repeated the same comment and then threw a soft drink on her, Mrs. Threat testified.

"Please leave me alone. I don't want to have anything to do with you," Mrs. Threat testified she told the man.

Threat then ran to the car and said: "You leave my wife alone."

A fight ensued and Verduin testified he ran over to the Nazis' car and started beating Threat because he said Threat was hitting a man who was pinned inside the car.

During the fistfight which lasted between five and seven minutes, as many as 35 uniformed Nazis, armed with riot gear and billy clubs, came from their headquarters across the street to the gas station, Threat testified.

"You black bastard. Why couldn't you marry a black woman or a Negro woman or something like that?" Threat said the Nazis shouted at him as three men were slugging him on his face with their fists. "Why are you beating on these white people?" Threat said the Nazis yelled at him.

Threat said he then yelled that he was a police officer and waved his badge to the crowd. By that time Arlington County police had arrived, Threat said.

Judge Richard Corman found Verduin guilty of assault and battery against Threat and destruction of Threat's eyeglasses. For each county, Verduin was sentenced to serve 10 days in the county jail and pay a $100 fine. Verduin said he will appeal the case to the Arlington Circuit Court.

The Army has not decided what action, if any, to take against Verduin, but the Army spokesman said his 20-day jail term will be counted as unexcused time.

A Chicago man, Robert F. Bukowy, was convicted Sept. 9 of assault and battery on Threat and Threat's wife and destruction of Threat's eyeglasses. Threat's wife testified that when she tried to pull one of the men off her husband, Bukowy kicked her in the back and on the arm. He was sentenced to a total of 12 months and five days in jail, with all but six months suspended.

A third man, Sean McQuire of Pasadena, Tex., is at large and Arlington police have filed an assault warrant for his arrest in the incident, according to Assistant Arlington Commonwealth's Attorney William Nunn.