Federal prosecutors in Baltimore have extended their political corruption investigations into yet another part of Maryland by issuing a sweeping group of subpoenas for the financial records of Harford County Executive Charles B. Anderson Jr.

Federal subpoenas also were served last week on officials of the north-eastern Maryland county for records and buliding permits negotiated during the four years of Anderson's administration.

Last week's subpoenas make Harford County the fourth Baltimore-area jurisdiction to fall under the scrutiny of federal prosecutors since the U.S. Attorney's Office in Baltimore started a series of probes into local governments nearly five years ago.

The subpoenas arrived only a few days after Maryland Gov. Marvin Mandel was convicted in Baltimore federal court of mail fraud and racketeering after a three-month trial.

During the five years of investigations, the county executives of both Baltimore County and Anne Arundel County have been sent to federal prison after they were convicted of extortion and bribery charges.

The same investigation also led to the resignation of former Vice President Spiro T. Agnew, who rose to national office after holding the posts of Baltimore County executive and governor of Maryland. In 1973, Agnew pleaded no contest to a single count of tax evasion stemming from the investigation.

Federal prosecutors have been investigating contract awards in the Baltimore city government as Well.

The three counties touched by probes - Baltimore County, Anne Arundel County and now Harford - are part of a ring around the city of Baltimore.

Of all of them, Harford County - Which stretches from the northern Baltimore suburbs northeastward to the Susquehanna River and the Pennsylvania prospect for future development.

Charles Anderson - who is not related to Dale Anderson, the convicted former Baltimore County executive - became Harfoed County's first executive in January, 1973, when the subdivision began charter government. Anderson's administration has been marked by a series of controversis involving awards of county contracts to developers.

Anderson could not be reached for comment. His lawyer, Peter Parker, said he has had no contact with the U.S. Attorney's Office in Baltimore and added that Anderson's personal records have not been subpoenaed.

Because of the broad sweep of last week's subpoenas, it is impossible to determine the thrust of the federal investigation. Assistant U.S. Attorney Daniel Goldstein refused comment, saying, "This office does not comment on grand jury investigations."

The subpoenas went to the county's treasurer, the head of licensing and permits and the clerk of the county's Circuit Court, accoring to County Attorney John E. Kelly and court officials.

The two subpoenas to administration officials, Kelly said, cover every county contract larger than $2,500 negotiated during Anderson's term as well as every building permit issued in the four-year period.

Kelly said county officials will comply with the subpoenas, which call for delivery of the records by September 12.

The third subpoena covers all reords of real estate transactions, limited partnerships, inheritances and financing statements for Anderson and 15 other companies and persons, including Mervyn G. Thompson, the county's zoning administrator.

Two of the business ventured listed in the subpoena are partly owned by Anderson, according to informed sources. They were placed in a blind trust by Anderson after he became county executive in 1973, the sources said.

The subpoena - which covers the period from 1960 to present - also seeks records of Bernard P. Kole, who heads the Baltimore City state's attorney's major fraud unit and lives in Harford County, and other Harfold County figures.

Anderson, a boyish-looking, 46-year old dark-haired man, one of five Harford County Commissioners before being elected executive, has developed a reputation for being cool toward the press and generally resistant to demands of the present Council.

Two controversies during Anderson's long-running feud with the County Council have attracted more attention and generated more lawsuits and bitterness than any others.

Earlier this year, Anderson defied a County Council vote and appointed an engineering firm of his own choosing to oversee contruction of the proposed Sod Run Sewage Treatment plant, which is to be located in the southeastern corner of the county.

Instead of giving the design contract for the plant to the firm that the County Council chose. Anderson instead assigned the contract to Century Engineering, a Baltimore County firm. The Sod Run plant, which would greatly expand development opportunities in the area, is also the largest public works project in the county's history.

Earlier, Anderson and the Council had clashed over the selction of a site and an architect for the proposed new courthouse in the county seat of Bel Air.

During the series of federal probes into local governments, the federal prosecutors in Baltimore have most often concentrated their efforts in the suburban counties where the pace of development has been more rapid than anywhere else.

As the suburbs expand, there is a pressing need for such public-works projects as roads and sewers. In addition, there is pressure for revision of the zoning regulations and for the expansion and modernization of county government facilities.

In the earlier probes in Anne Arundel and Baltimore counties, county officials were convicted of taking kickbacks from the architects and engineers who designed and helped work on county projects.