Investigators for Prince George's County State's Attorney Alex Williams are interviewing people who have complained about several land transactions involving the county government.

The inquiries come after a new round of citizen complaints to a local grand jury alleging that politically active developers have received favored treatment in land sales and other transactions with the county government.

Two detectives, including veteran investigator Alonzo D. Black, met yesterday with Hyattsville lawyer James Casey, a landowner who has publicly questioned the county's property sales in the Collington Center industrial park on Route 301 near Upper Marlboro. Casey said he provided some materials to the investigators, who asked "very preliminary" questions.

The detectives also contacted a lawyer familiar with the county's purchase of a $3 million office building in Upper Marlboro from a partnership that includes the county's director of public works and a major campaign supporter of County Executive Parris N. Glendening.

Williams yesterday would neither confirm nor deny that an investigation is underway.

But he said his economics crimes unit, in which Black is a senior investigator, has closely reviewed recent newspaper articles detailing some of the transactions and has received new complaints from residents.

"Allegations have come our way and we've reviewed them and we take them very seriously," Williams said.

But, he said, "It's a bit early to come to any conclusions" about whether the transactions warrant further scrutiny.

Glendening could not be reached for comment yesterday afternoon.

Williams came under fire from a previous grand jury this year for offering little assistance in its independent probe of several county land transactions.

Frustrated by what they considered Williams's lack of interest, the grand jury members, who convened in October 1989, undertook the probe without prosecutorial guidance and finally sought legal advice from the office of State Prosecutor Stephen Montanarelli.

Both Montanarelli and Williams advised the grand jury not to bring indictments, and the group disbanded in March after issuing a report highly critical of the county's handling of a land swap and land purchases involving former Maryland secretary of state Fred Wineland, the father of council member Kirwan F. Wineland.

Since that time, county activists have appealed to a new grand jury to look into new allegations of favored treatment to Glendening's political supporters.

Casey and several others also have lodged complaints with the office of U.S. Attorney Breckinridge L. Willcox, who is conducting a preliminary review of materials on the Collington Center sales and several other county land transactions.

Casey, who is suing the county over the zoning on land he owns in the Route 301 median, alleges that the Collington Center sales were "giveaways" that deprived taxpayers of millions in revenue.

Glendening has described Casey as an embittered property owner who is seeking vengeance on the county. He has defended the Collington Center sales as proper and says the project put unused land back on the tax rolls and created hundreds of jobs.

Williams, who is seeking reelection, said that his office's interest in the land matters has no relationship to his political contest. "We don't make decisions in this office based on politics," he said.