A 10-year-old plan for a senior citizens' center in Rockville came a step closer to realization this week, as city lawmakers voted to set aside $100,000 in municipal funds and to seek a matching state grant for the project. $1

The center, planned for the former Woodley Gardens School, will offer recreation and social programs for Rockville's elderly population, now about 6,000 and growing rapidly, according to census figures. Ron Olson, city parks director, said the center could be open by the end of this year.

Jean Brady, who chairs the city's senior citizens commission, said she was delighted by the council's unanimous vote to finance the center project. "We've waited a long time for this," she added.

In other business, the council dropped its plan to allow the division of single-family houses into two dwellings. The idea had been under consideration as a solution to Rockville's growing shortage of rental housing, and as a way of easing property-ownership costs for older homeowners.

A majority of the city's citizen associations were opposed to such a zoning change, however. Opponents warned that it would bring excessive traffic to their neighborhoods, and would depress property values.