Robert S. McGarry has decided to quit his job as top executive of the sewer and water agency that serves Montgomery and Prince George's counties because of persistent feuding between the two county governments, McGarry's associates said yesterday.

McGarry, who is paid $50,000 a year as general manager of the Washington Suburban Sanitary Commission, is "fed up" with the feuding between the commissioners from the two counties who oversee the agency, according to Commission Chairman David Scotten.

Scotten said McGarry told him Wednesday he is not interested in negotiating a new contract when his current one expires in May.

McGarry, who has been with the WSSC for three years, would not comment yesterday. "I don't want to say anything until I've talked to all the commissioners. I've told (them) I will announce my intentions next week."

Scotten said that just a month ago McGarry indicated he wanted to renew his contract for a second three years.

Recent conflicts between Prince George's and Montgomery over the funding of WSSC projects and reports that the Prince George's County executive and council were unhappy with his performance led McGarry to change his mind, Scotten said.

The WSSC is run by six commissioners, three appointed by each county government. In the last nine months, the commission has been split along county lines on almost every major issue, including rate increases, the agency's budget, sewer capacity and sludge disposal. As a result, decisions that McGarry and the counties would like to see resolved officials said yesterday.

"I think he felt extreme frustration trying to run the agency like a professional and continually running into politics," Sally Kanchugar, one of the Montgomery commissioners, said yesterday.

Prince George's officials also acknowledged the difficulties of the position. "If you put Jesus Christ himself in there with Mohammand as his adviser, you would still have problems," said County Council Chairman Parris Glendening. The general manager "has to work for two sets of commissioners, two executives and two councils and that gets political, Glendenings said.

County and WSSC officials said that when the subject of renegotiating McGarry's contract came up recently it became another issue between the counties, with Montgomery officials favoring an immediate new contract and Prince George's officials wanting more discussion.

Scotten, who is from Montgomery said he thought Prince George's was "just trying to hold (McGarry's) contract hostage for some sort of quid pro quo.I want to let the public know what we have to deal with those crazy people in Prince George's . . . I see this as the beginning of the end for the WSSC. The agency is increasingly in disarray . . . No one of any competence will come here."

Prince George's officials denied Scotten's charge and said they wanted the delay to allow various county officials to discuss McGarry's tenure and whether the county's interests have been handled well under him.