The controversy surrounding management consulting contracts for construction projects in Essex County expanded this week as a county prosecutor entered the case and the county tried to cancel the contracts in question.

The Essex County district attorney's office is now investigating the perhaps questionable relationship between the Essex County Commissioners and PCM, Inc., a New York management consulting firm that the commissioners hired in 1974 to supervise more than $10 million in county construction projects.

Howard Camuso, first assistant district attorney in Essex County, said yesterday, "We're inquiring into certain aspects of the PCM contract. Right now we're just listening to what people are telling us."

The county commissioners voted Tuesday to void their contract with PCM because the county learned that PCM was never legally registered to do business in Massachusetts.

PCM was organized in Delaware in 1974, but failed to pay its franchise tax that year, and was voided as a Delaware corporation on March 1, 1976. Because PCM was voided in Delaware, its Massachusetts registration is also voided.

Officials in the Delaware corporation office said yesterday that PCM owed the state a total of $54.95 in 1974 taxes, penalties, and interest.

The contracts with Essex County would have been worth about $300,000.

County Commissioner Edward H. Cahill of Lynn, who made the motion to void PCM's contract, said yesterday that newspaper articles about PCM and its connections with another New York consulting firm that allegedly made payoffs to two Massachusetts state senators, caused the commissioners to seek an end to the contract.

"There was so much talk and publicity about the contract with PCM we decided that if this is an opportunity to cancel the contract, then we should take it," Cahill said.

Two men who in 1974 were top executives of PCM, William F. Harding and Daniel J. Shields, were named as go-betweens in federal extortion indictments this summer against the two state senators, Joseph J.C. DiCarlo of Revere and Ronald MacKenzie of Burlington.

Adek Apfelbaum, a spokesman for PMC in Great Neck, New York, refused to comment yesterday on PCM's Essex County contract, but said he did not know of the commissioners' vote to cancel the contract.

Peter F. Brady of Lynn, PCM's local attorney, said yesterday he had not yet seen the commissioners' letter cancelling the contract as of March 1, 1976, and refused to comment further.

Essex County Treasurer Thomas F. Duffy sued the commissioners and PCM in 1975, charging that PCM would duplicate the services provided by the state bureau of building construction.

Brady was PCM's attorney in that suit, and he and Cahill agreed that the cancellation would have no effect on Duffy's suit. Duffy refused to pay PCM's first bill to the county of $16,000 in 1975.

A spokesman for Atty. Gen. Francis X. Bellotti, who as a private citizen in 1974 was PCM's local attorney, said yesterday Bellotti would not comment on the PCM investigation or the commissioners' attempt to cancel the contract.

William S. Wasserman Jr. '48, publisher and columnist for the North Shore Weeklies, who first reported PCM's failure to pay its Delaware taxes, said yesterday he thought the commissioner's action was "appropriate."

Wasserman said however, "There are many other unanswered questions about why this firm came to Essex County."

John W. McKean '71, a Democratic nominee for Essex County Commissioner who pledged last month to investigate the PCM contract said yesterday the commissioners' vote Tuesday does not change his plans