A retired FBI agent from Silver Spring pleaded guilty to tax evasion yesterday in Baltimore federal court.

Frederick J. Dobbratz, 64, of 14000 Castle Blvd., Silver Spring, admitted to U.S. District Court Judge Joseph C. Howard that he failed to report his 1979 income of $17,538 from his federal pension. An IRS spokesman said that Dobbratz, who retired from the FBI in 1968 after 28 years of service, evaded taxes on a total of $61,940 from his federal pension, for the years 1976 through 1979, on which he owes $15,221 in federal income tax.

Dobbratz, who was released without bond, faces up to five years in prison and a maximum fine of $10,000, according to IRS spokesman Domenic J. LaPonzina. No date has been set for sentencing.

In a second tax case, James William Campbell, 37, a barber, of 14635 Delano Dr., Woodbridge, Va., appeared before U.S. District Court Judge James R. Miller Jr. in Baltimore Thursday night and pleaded guilty to one of seven counts of making false claims for a tax refund.

Campbell gave the court checks of $4,064 made out to the IRS and $3,963 to the comptroller of Maryland, as restitution for refunds he received as the result of false refunds he claimed on his 1980 tax returns, according to the IRS.

Campbell was released on $2,500 bond, pending sentencing on June 17. He, too, could be jailed up to five years and fined up to $10,000