A Virginia man pleaded guilty yesterday and a codefendant pleaded innocent to federal conspiracy charges involving an alleged East Coast drug-smuggling ring that prosecutors said netted $30 million over eight years.

The guilty plea by Kevin B. Munley, 34, of Fairfax County was accepted by District Judge James C. Cacheris during a brief hearing in federal court in Alexandria. Cacheris set sentencing for Munley, who faces up to 20 years in prison and a $25,000 fine, for Jan. 21.

Both Munley and codefendant Barry Wayne Toombs were extradited earlier this week from Costa Rica. Trial for Toombs, described as a leader of the alleged ring, was set for Feb. 7 in Alexandria.

A third defendant, William L. Popwell, 36, of Mckenzie, Ala., an alleged boat crew member for the ring, was sentenced yesterday by District Judge Richard L. Williams to five years in prison with all but six months suspended.

The three men are among 20 defendants indicted earlier this year following a tax and drug investigation by federal authorities.

Three defendants are in custody in Costa Rica, where they are fighting extradition to the United States. The others are either awaiting sentencing in the case or are still at large, prosecutors said.