A 58-year-old Potomac lawyer pleaded guilty in federal court here yesterday to a felony charge of receiving stolen goods in connection with the operation of the largest gold and silver fencing operation ever uncovered in Washington.

Carl P. Fogel of 11915 Seven Locks Rd. entered the plea after jury selection had begun for his trial on 14 criminal charges, including conspiracy to operate a racketeering-influenced criminal operation.

His attorney, Kenneth Robinson, told U.S. District Judge John H. Pratt that Fogel would resign from the bar when he is sentenced Sept. 2. Fogel, free on personal recognizance, could be sentenced to up to 10 years and fined up to $1,000.

The charges stemmed from an exhaustive federal undercover operation known as Operation Greenthumb that focused on a fencing business operated by Joseph Martin out of Royal Carpet and Tile at 1785 Florida Ave. NW.

Assistant U.S. Attorney Roger H. Adelman said in court that the government would have proved that Fogel was aware of Martin's involvement in the fencing operation and did nothing to stop it. Adelman said that Fogel was present when a woman named Angela Walker sold Martin several rings she had stolen from W. Bell & Co., where she worked, and that Fogel saw Martin remove W. Bell tags from the rings.

In March 1981, Adelman said, Fogel received a gold ring from Martin that he knew Walker had stolen. Adelman said tape recordings showed Fogel's involvement.

Saying he was pleading guilty "because I think the tapes would show . . . that I knew that Joseph Martin was a thief and I didn't do anything about it . . . ," Fogel said, "I can't confront myself other than to tell the truth." He asked Pratt to delay sentencing until he could complete two pending cases and train his partner to take over his practice.

Martin was sentenced in 1982 to eight years after he was convicted of racketeering and tax evasion, and has since been released from prison. Walker was sentenced to probation.