The 24-man building inspectors force in Baltimore County has been under investigation by the county government and the state's attorney's office as part of a continuing effort to clean up an image that lingers in the wake of ex-Vice President Spiro T. Agnew and his successor as county executive, Dale Anderson, county officials say.

Agnew pleaded nolo contendere to income tax evasion charges and Anderson was convicted on extortion and kickback charges. Both men were accused of granting favors to developers and their fiends, accusations that could imply cooperation by county building inspectors, said John D. Seyffert, head of the Baltimore County Department of Licenses and Permits.

Earlier this month, building inspector Francis McKenna was convicted for accepting plumbing supplies in return for giving special consideration to The Ryland Group for a housing development called Woodbridge Valley the firm is building in Catonsville, Md. A Ryland Group building supervisor was given imunity from prosecution for cooperating in the investigation, which began with information from an informant, officials said.

McKenna, 55, of Parkville, Md., pleaded guilty before Judge William Hinkel in Baltimore County District Court to charges of obstructing justice by covering up the bribe he accepted and falsifying reports. Sentenced to one year probation, McKenna lost his job and his right to a pension.

Sandra O'Connor, state's attorney for Baltimore County, said McKenna allegedly demanded $220 worth of plumbing supplies from a building supervisor for the Ryland supervisor gave McKennabout $30 worth of plumbing supplies, O'Connor said.

In addition to the McKenna case, administrative actions are pending against three other building inspectors, who face possible dismissal from their jobs for alleged "sloppy inspections" of housing developments in the county. They have not been accused of involvement with bribes.

"Historically the building inspectors and the entire department of licensing and permits were subject to allegations that the two former county executives, Agnew and Anderson, gave favors to developers and their friends," said Seyffert.

"When I took over I set myself a goal of one year to try to make it (the department) more professional.It's been two and a half years now and I'm still at it."

Seyffert, who was a development director for the House Co. for five years, will be the one who decides within the next two weeks what sanctions will be taken against three inspectors.

The three are charged with violating personnel rules and regulations of the county, including rules regarding falsification of records, time sheets and reports.

"If there wre outright gift-takings, it probably would have been handled by the state's attorney as a criminal offense," Seyffert said.

Marion McCoy, physical growth coordinator for the county, said "word got out some time ago" that something was wrong in the inspections department.

County building inspectors are required to check five elements of onstruction-the footings, foundation, basement floor, framing and final work coordinating the electrical, plumbing and settlement controls-to insure that a house is safe and meets the county building code before an occupancy permit is issued.

With new housing in heavy demand, allegations have circulated that builders have tried to rush through the job and pay off inspectors for not noticing shoddy workmanship, Seyffert said.

It has also been alledged that that inspectors are often political appointees who may not be qualified for the job, he added.

"I have to choose my work carefully," the department head said, "because I've heard a lot of allegations but I really don't have proof of any wrongdoing. But historically the director of this department was a political plum appointment. They never devoted much time to directing or managing.

"The majority of inspectors were good political people who worked in the campaigns for county executive," Seyffert added.

Most of the 66 housing, settlement control, electrical and plumbing inspectors in the department have been on the job for more than a decade, Seyffert said. The four who are charged with wrong-going are among the veterans in the department, he added.

"I was appointed to wipe out those allegations or thoughts (of wrongdoing or favoritism)," Seyffert said.

Seyffert, who took over his job in February, 1975, said he has set up a rotation system for inspectors and a daily planning schedule to keep tabs on what inspectors are doing and who they are dealing with. The rotation procedure helps prevents the inspectors from developing close relationships with individual builders, Seyffert maintains.

Historically the inspectors were assigned in areas where they had some political clout," Seyffert said. "Now every six to 10 months they rotate."