The Rockville City Council voted Monday to extend until April the building moratorium it imposed in July along a 1 1/2-mile stretch of Rockville Pike, one of Montgomery County's most congested arteries.

The vote followed the presentation last week of a consultant's report warning that traffic flow will become seriously impaired at rush hours if construction is not restricted.

The extension will allow city officials time to study the report and possibly implement some of its recommendations.

Based on a six-month study of traffic and development conditions by JHK & Associates, the report says that the stretch of the Pike in Rockville between Veirs Mill Road and Twinbrook Parkway can accommodate only about 4.2 million square feet of new development. Under existing zoning, up to 6.5 million square feet of development is possible.

Among the report's recommendations for easing traffic conditions is the extension of East Jefferson Street from Congressional Lane to Edmondston Drive. The extension would run parallel to the Pike.

The council imposed the seven-month moratorium in July after the city planning staff reported that upwards of 1.3 million square feet of office and commercial space might be built along Rockville Pike in the fiscal year then starting. The staff said that such growth would exacerbate traffic along the corridor and strain sewer service.

The moratorium applies only to development that would generate additional traffic along the Pike. Remodeling or reuse of existing buildings on the Pike is permitted where no additional parking spaces are needed.

The busy strip of automotive, commercial and retail outlets has seen intense development over the years, particularly at the southern end.