Montgomery County members of the House of Delegates, saying their local government has failed to manage the county's growth, approved legislation today that would strip the County Council of two prized prerogatives in land use planning.

As rival representatives of County Executive Charles W. Gilchrist and the council watched anxiously, the delegation voted 12 to 9 to give Gilchrist's successor new power to appoint two members of the local planning board.

And in a 12-to-8 vote, the delegation approved a measure that would give future Montgomery County executives new veto power over master land use plans, the basic blueprints for development in the affluent suburb.

The two local bills have passed Montgomery's state Senate delegation. Because they affect the Maryland-National Capital Park and Planning Commission, an agency with planning duties for Montgomery and Prince George's counties, they also must be passed by Prince George's County's legislative delegation, which is expected to give the changes routine approval.

Endorsement by the Prince George's delegation would send the measures to the full House and Senate for consideration.

"We have an expression down here that if something ain't broke you don't fix it," said Del. Judith C. Toth (D-Montgomery). "But if you live in the upcounty, you know the system's broke."

Toth's remarks summed up the feeling of most of the supporters of the two bills, which were drafted by Gilchrist's office and were objects of intense lobbying efforts this week by the county executive and the council.

Gilchrist has sparred repeatedly with the council since taking office in 1978 and recently blamed the current system of land use planning, which is dominated by the council and planning board (Montgomery's half of the bicounty planning commission) for the congestion in the Rockville-Gaithersburg area and other portions of Montgomery.

Council members have long prized their traditional power to appoint all five planning board members, and several delegates complained that they were caught in yet another political squabble between the council and Gilchrist.

"If the executive and council could get along, all of this wouldn't be in Annapolis today," said Del. Mary H. Boergers (D-Montgomery).

The bills' opponents, led by Del. Donald B. Robertson (D-Montgomery), argued that the changes violated the spirit and letter of the county charter, which puts most land planning powers in the hands of the council and planning board.

Passing the bills seven months before local elections in which development is sure to be an issue would "destroy the charter with a last-minute political compromise," said Robertson.

"We're doing something hastily to solve a political problem," he added.

Robertson's colleagues rejected his three attempts today to dilute or kill the bills.