Realtor John P. (Jack) Hewitt, a former Democratic candidate for Montgomery County executive now running for that office as a Republican, yesterday unveiled a slate of five council running mates who Hewitt said would bring business-style management to county government.

Hewitt, one of three Republican candidates seeking to challenge the expected Democratic nominee, incumbent Charles W. Gilchrist, is hoping formation of the slate will quash suggestions by opponents that he does not have support in a party he just joined in May.

At a noon press conference, Hewitt said he was "tickled to death" with his running mates, who he said represent the mainstream Republican business-oriented philosophy of less government and more private-sector incentives.

"Our appeal to the electorate will be based on a commitment to bring a business-like approach to the management . . . of Montgomery County," Hewitt said.

Running with Hewitt are: Albert Ceccone, an investment counselor; John A. Dean, attorney; Malcolm Lawrence, a consultant and former foreign service officer; James A. Rose Jr., consultant, and Alan S. Zipp, an accountant. None has ever held elected office.

Del. Luiz R. Simmons, a more moderate Republican candidate for executive, said, "This particular slate does nothing to enhance his Hewitt's prospects in the Republican primary. Hewitt's first attempt to get the party to endorse him was rejected and now he's kind of floundering around looking for a pseudo-event."

Simmons said he will not be forming a slate because, "I don't want to stuff a slate down anyone's throat."

The third GOP contender, banker Joseph McGrath, who could not be reached for comment, reportedly is searching for running mates.

Hewitt said members of his slate generally support President Reagan and his economic program, but emphasized that they want to make the incumbent county Democrats, especially Gilchrist, their key issue.