Baltimore County Executive Theodore G. Venetoulis, a candidate in the Maryland gubernatorial race, said yesterday that he now regrets hiring a private detective firm in 1973 to investigate whether business rival had ties to organized crime.

Venetoulis was responding to a report published in The Baltimore Evening Sun yesterday saying that, wher Venetoulis was a private businessman competing for a cable television franchise in Baltimore County, the company he headed hired Interstate Bureau of Investigation, Inc. to investigate the head of a rival firm.

Venetoulis' firm, Community Cablevisions Inc., hired the detectives, Venetoulis said, because a book had been published in which his rivals name had been connected to "so-called mobster loans."

Community Cablevision lost the bid to the rival company, Calvert Telecommunications Inc. A Venetoulis spokesman said yesterday that the information gathered by the detectives never was made public because Venetoulis and his associates thought it was not noteworthy.

After losing that bid, Venetoulis went into electoral politics, winning the 1974 race for county executive and contending now for the Democratic gubernatorial nomination in Maryland.

The newspaper report was accompanied by an editorial that suggested Venetoulis should "call back (his) private eye into action, this time to scrutinize the Ventoulis challengers and find out which one loosed the blood-hounds on this aging but shabby trial."

The detective firm, owned by Marshall M. Meyer, also did an investigation for suspended Maryland Gov. Marvin Mandel when he suspected that his office telephones were being tapped.

During his 1974 county race, Venetoulis continually was asked to answer questions about the controversial cable television battle with Calvert. The use of private detectives was not known until now, however.