The Supreme Court ruled 7 to 1 yesterday that U.S. authorities can prosecute a convicted felon for possessing guns that had crossed state lines before he became a felon.

The decision affirmed the convictim - under the federal Omnibus Crime Control and Safe Streets Act of 1968 - of Richard A. Scarborough of Fairfax County.

The law provides up to two years in prison and a fine of up to $10,000 for anyone who has been convicted of a felony and who later "receives, possesses, or transports in commerce or affecting commerce . . . any firearm."

Scarborough became a felon in September, 1972, when he pleaded guilty in Fairfax County to possession of narcotics with intent to distribute.

Almost a year later, county police arrested him on a new narcotics charge and got a warrant to search him home near Falls Church solely for drugs - but they went to this home with a federal Treasury agent who came to look for firearms.

The federal agent found in Scarborough's bedroom an M-1 carbine that enetered Virginia after moving from Illinois to Maryland in 1966, and three pistols, including one made in France in 1892. The pistols had moved in interstate commerce several years earlier.

Scarborough was convicted and sentenced. The Fourth U.S. Circuit Court of Appeals upheld the conviction and it was affirmed yesterday in an opinion for the Supreme Court by Justice Thurgood Marshall.

The lone dissenter, Justice Potter Stewart, wrote that Congress did not mandate the courts to construe the crime act "so that a person in lawful possession of a firearm, and proved to be innocent of a felony until proven guilty, must upon his conviction of a felony also be automatically and instantly guilty of a wholly different serious criminal offense."

He said that under the majority ruling, "a bookkeeper who owns a hunting rifle and who later commits embezzlement will, immediately upon his embezzlement conviction, also be guilty of violating" the crime act.

Justice William H. Rehnquist did not participate in the consideration or judgment of the case.