A federal judge in Alexandria sentenced a past president of a Northern Virginia branch of the Pagans motorcycle gang to seven years in prison for a firearms violation yesterday, using a special statute permitting the addition of five years to the normal two-year maximum for the offense.

U.S. District Judge Albert V. Bryan Jr. invoked the 1970 "dangerous special offender" law, determining that the defendant, Richard Allen Scarborough (nicknamed Friar Tuck during his years with the Pagans), is "dangerous" to society.

"There is no question that a longer period of confinement is needed . . . in order to protect the public," Bryan said of Scarborough, who was convicted by a jury last month of possession of a firearm by a convicted felon.

The latest conviction for Scarborough, who has eight previous drug-related or firearms convictions, was in a case in which he was accused of entering an apartment in Fairfax City and brandishing a firearm after he found his wife in bed with another man.

Yesterday, Scarborough tearfully pleaded for leniency, saying: "I love my family so much. I thought I was doing the right thing. I was fighting for my family . . . . "

According to court papers, Scarborough was president of the Pagans in 1970 and pleaded guilty that year to being an accessory to the abduction of two members of the rival Saints motorcycle gang who were later killed.

Scarborough said he left the Pagans after the slayings because the gang had changed from the time when it was "a bunch of guys who got together on weekends and went to races with their wives and girlfriends . . . . "