Three former mid-level General Services Administration employes pleaded guilty yesterday to taking thousands of dollars' worth of kick-back -- in cash, clothing and home repairs -- from maintenance firs doing business with the federal government.

In return for the payoffs, the three men, James N. Henslee, 32; Elmer A. Van Pelt, 60, and Robert M. Bryant, 31, approved inflated GSA maintenance contracts, according to their guilty pleas. They conspired with private maintenance contactors through "craft, trickery, deceit and dishonest means" to thwart normal repair and maintenance procedures.

Their guilty pleas brought to 30 the number of former GSA workers who now have been found guilty of various charges in the ever-widening federal corruption investigation of the government's landlord and office supply agency.

Assistant U.S. Attorney William S. Block told U.S. District Court Judge Oliver Gasch that Henslee, Van Pelt and Bryant are all cooperating with government investigators probing the GSA scandals and are expected to testify at grand jury hearings and upcoming trials.

But Block later declined to say whether the three have implicated other GSA officials or private contractors.

According to the criminalk informations to which they pleaded guilty, Henslee, Van Pelt and Bryant approved maintenance contracts at inflated values so that the cost of the repair work wa sconvered as well as the kickbacks to the GSA employes.

Henslee engaged in the conspiracy with undisclosed contractors from Jan. 1, 1974, to June 30, 1977, and received kickbacks worth between $50,000 and $75,000, according to the criminal information.

In addition, Henslee pleaded guilty to filing a false claim with GSA for a $1,970 janitorial services contract. Henslee, of 3103 Pershing Dr., Arlington, worked at GSA nas a carpemtry supervisor for 12 years until he resigned in November. He now faces up to 10 years in prison and a $20,000 fine.

Bryant, who now lives in Dunedin, Fla., resigned last August after working as a building manager since 1971. He received kickbacks worth about $5,000, according to Block, and now faces up to five years in prison and a $10,000 fine.

Van Pelt, of Mechanicsville, Md., retired on disability last April after working 25 years at GSA. He allegedly got kickbacks worth more than $35,000. He approved a foor tile contract with John P. Rudell, a contractor who previously pleaded guilty to defrauding the government as part of a scheme in which $900,000 in kickbacks were paid to GSA employes.

In a separate case, Doretha R. Black-well, 4-, an assistant manager of a GSA self-service office supply store in Baltimore, pleaded guilty Tuesday to conspiracy to defraud the government. She had pleaded innocent to charges of receiving gifts from Matthew Christopher Associates Inc., in return for submitting fraudulent invoices to GSA officials.

Assistant U.S. Attorney Daniel Clements said he will recommend a two-month prison sentence for Blackwell.