Shady Grove area residents who fear that already jammed roads may be unable to support billions of dollars in new development proposed west of I-270 remain disturbed by a rezoning plan currently before the Montgomery County Council.

They say that county planners have not provided adequate projections, that a patchy, indefinite construction schedule will leave bottlenecks on crucial portions of main roads as population climbs, and that the only safety valve--a county law designed to prevent development beyond what the roads can accommodate--has already failed to protect them.

Issues of density, agricultural preservation and the Mixed-Use Planned Development zoning that marks whole tracts open to unspecified, high-density development still linger. But the road system forms the basis of the development plan, and planners, residents and officials alike have singled out roads as the most immediate and most basic concern.

The designers of the rezoning--the Maryland-National Capital Park and Planning Commission--said in their report, "This plan is an end-state plan" that relies on the county's Adequate Public Facilities ordinance and periodic reviews of development thresholds to make sure that residential and commercial construction don't exceed what the roads can support.

The ordinance states that development cannot be approved unless the roads are there to serve it. But the ordinance allows planned roads--if they are scheduled for construction and if 50 percent of their cost is budgeted--to be counted as if they existed.

Muddy Branch Road is often singled out as a case where the ordinance has failed. County maps in 1971 list it as a "major highway" connecting the western Route 28 area to Gaithersburg, and construction money has been there for years. However, while new subdivisions that rely on that road have been steadily approved and built, Muddy Branch Road remains somewhat less than a major highway, with sections widened by developers narrowing down at points to a shoulderless country lane. Currently, a daily bumper-to-bumper procession jams the road.

City council members from Gaithersburg and Rockville met this week with the Maryland-National Capital Park and Planning Commission staff who prepared the rezoning, discussing most specifically traffic in the Shady Grove area.

"Our council is still concerned about implementation of the plan for increased density in advance of the roads," said Gaithersburg Planning Director Jennifer Russel. "It all boils down to traffic. They are concerned about the adequacy of the Adequate Public Facilities Ordinance."

Russel said the City Council plans to ask the county council to make approval of new subdivisions and commercial projects dependent on actual, complete roads when hearings begin Nov. 8. Perry Berman, planning supervisor for northern Montgomery, said the county planning board is also preparing suggestions for the council that would strengthen the adequate public facilities law. The council has the ultimate authority to establish zoning.

The master plan calls for thousands of housing units and millions of square feet in commercial space in a 2.7 mile zone between Rockville and Gaithersburg that officials describe as a third city, "Rockburg." It is expected to bring in 20 years 77,000 new employes--2 1/2 times the number currently working in Rockville to an area one-fourth its size, according to figures Jeffery L. Ruben, chairman of Gaithersburg's Planning Commission, presented at hearings in April.

"We recognize that growth has to take place, and we'll accept that," said Diane Aronson, vice president of Westleigh Civic Association, which represents a subdivision on west Route 28. "But we aren't going to accept a road network that can't handle it, and we aren't going to accept densities that" exceed existing road capacities, she said. Berman said some residents "assume that all the development projected will happen all at once. We don't assume that. We think it will be stretched over time, roughly about the same period" roads are built, he said.

The county's zoning plan calls for a denser zoning around Gaithersburg. It would establish along the I-270 corridor extensive acreage for "mixed-use" complexes, where high-rise clusters of offices, businesses and condominiums, apartments and town houses between Rockville and Gaithersburg.

Critics of the Gaithersburg vicinity master plan, as it is officially known, noted that a recent Metropolitan Washington Council of Governments report showed increased car commuting despite the subway, and said county plans that count on relief from Metro may turn out to be too optimistic.

Roundtrip fare from Shady Grove to downtown currently is expected to cost $5.50. "With parking, that's $6.50 a day," said Gerald E. Levine, a member of Dufief Home Owners Association. "A three-person car pool can do it for $3 a day. A lot of people aren't going to ride Metro, it's as simple as that."

Planners intend to sweep traffic onto major roads that will put Washington commuters onto I-270 and provide quick access to the Shady Grove Metro subway station. Those roads will also ensure mobility for people projected to fill the area between the Rockville and Gaithersburg, planners said.

"Future development in much of this planning area is highly dependent upon timely construction of a number of roads," planners said in their report. I-370, which would connect the Shady Grove Metrorail station with I-270; Key West Avenue, designed to peel subway-bound traffic from Route 28 west of I-270, and an "Eastern Arterial" intended to ease the jams of commuters around Shady Grove Village east of I-270--these are among the principal roadways in the plan.

Some residents and officials said they believe the road system will smooth out after 1990. But in the meantime, they project--and officials concede--that portions of key routes will develop piecemeal, partly because not all the segments are under county jurisdiction. They say that compromises traffic control.

Russel noted that the segment of the Eastern Arterial between Goshen Road and Route 124 will not be ready with the rest of it. "It's going to be a crunch in the short term," said Alan Grant, a real estate lawyer and member of the Shady Grove Village Council.

Rte. 28, which is a state road but the one with the most severe traffic problems, has parts yet to be funded, Berman said. And I-370 "will not be operational by the time Metro opens--that's for sure," said Robert C. Merryman, chief of the county transportation department planners. He noted that some improvements, like a three-lane bridge span that would double the capacity of Shady Grove Road, are currently ready to be contracted.