The Montgomery County police union last night postponed until August a vote of no-confidence against Chief Donald E. Brooks after County Executive Sidney Kramer agreed in last-minute negotiations to spend $1.3 million for 66 new police cars.

The union, the Fraternal Order of Police, Lodge 35, called for the vote last week, citing "disenchantment" and frustration with Brooks's leadership, failures of the police radio system, a shortage of take-home cruisers and recruitment problems.

Walter Bader, the union's president, said last night the labor group agreed to delay the vote of no-confidence until its Aug. 18 meeting because of "good-faith discussions" with top county officials.

"We have some mutual dialogue starting between two sides," said Bader.

"We're hoping to begin anew . . . and forget what has happened before."

Bader said negotiations started Friday with Kramer and his top assistant, Lewis Roberts, the county's chief administrative officer. Talks continued on Sunday and Monday, he said.

Brooks was not involved in the talks, although Bader said he met with the chief Monday for three hours.

Last night, about 150 union members who attended a special meeting unanimously approved the decision to postpone the vote of no-confidence against Brooks, who was appointed chief in April 1988, said union official Don McClure.

The labor unit has about 800 members, officials said.

The union meeting, held in a hot hall in the rear of a Gaithersburg strip shopping center, lasted for about 90 minutes and was punctuated with loud clapping and cheering.

The meeting was closed to the news media.

Calling the county executive's promise of additional police cars "a very good first step," union leaders said they will take a wait-and-see position on resolving the other issues.

"If there is not a continuation, and this is a one-shot deal, then we may have another censure vote," said McClure.

Kramer indicated that he plans to ask the County Council this week to approve money for the additional cars, Bader said last night. Bader said most council members have indicated the request will be approved.

In the future, Bader said, the Fraternal Order of Police plans to hold negotiations with Lewis on economic matters, and negotiate with Chief Brooks on noneconomic subjects.