After years of rivalry, the new Rockville city and Montgomery County police chiefs appear to have begun an era of cooperation between their departments.

Jared (Jed) Stout, who six months ago became chief of Rockville's 20 uniformed officers, told the City Council this week that he and the county police chief, Bernard D. Crooke, are working together to strengthen both departments.

Stout's predecessor, Charles R. Wall, who resigned last spring to become police chief in Morgantown, W. Va., and former county chief Robert J. diGrazia were constantly at odds over the role of the city police force. DiGrazia maintained the city police were unnecessary and duplicated functions of the county department.

Stout and Crooke, however, have put that issue aside and now are working jointly to build a stronger city department to complement the county force, Stout told the city lawmakers.

Beginning next month, Stout said, city residents will be able to use the 911 emergency telephone number to reach city police. In the past, Rockville residents who called the emergency number got response from county police only. Residents had to call the city department directly to reach a city officer. Under the new policy, Stout said, the city or county officer nearest the scene of an emergency will respond to the call.

Nonemergency city calls, deferred by the county when no police unit is available, now will be referred to a city officer. Stout urged that residents use the 911 number for emergency calls only, and call the 24-hour city police number, 340-7300, for other reports.

Stout also said city police will step up enforcement of traffic laws, in response to complaints about speeding in certain parts of Rockville. Every day, Stout said, two to four radar-equipped patrol cars will be used to catch speeders in the city.

Stout, 43, was commander of planning and research for the Fairfax County Police Department before coming to Rockville.