Elizabeth Beall Banks, the Montgomery County farmer who drew wide public support two years ago when she feared a road improvement assessment of nearly $753,000 would spell the end for her century-old farm, has been hit with an even higher assessment for another road project.

Banks, 73, tentatively has been assessed $770,000 from the proposed three-mile widening and reconstruction of Muddy Branch Road, from Route 28 north to Gaithersburg, according to George Mosburger of Montgomery's Department of Transportation assessment division.

With the new assessment, which won't be final until the Muddy Branch Road improvements are finished in 1988, Banks could owe the county more than $1.5 million in improvements for roads she considers an assault on her farm.

"It's unbelievable," Banks said. "I'm being assessed about a million-and-a-half for roads I don't even want. Why should I pay for everybody driving around my property?"

The recent appraisal marks the latest turn in the intense tug-of-war between Banks -- who has fought to preserve the 135-acre farm off Route 28 that she single-handedly tends each day -- and county officials' efforts to upgrade the road network along traffic-choked Route 28.

In 1983, the county presented her with a $752,141.02 assessment as her share of the 3,000-foot-long, two-lane "relocation" of Route 28 called Key West Avenue. Officials maintain it would benefit her property by running a new state road over about six acres on her farm's east side.

Key West, a would-be off-shoot of Route 28 intended to divert some of the bumper-to-bumper Washington-bound suburban commuters, is scheduled to open this month. Upon the project's completion, targeted for this fall, Banks will receive a final assessment, which may be more or less than the one she got in 1983.

The $10.2 million widening of Muddy Branch Road, a two-lane road that will be turned into a four-lane divided highway, is scheduled to start next spring and to be completed two years later, said Robert C. Merryman, county chief of transportation engineering.

Road assessments, county officials said, are intended to compel property owners to share the cost of projects that would benefit them.

But Banks, a retired school teacher who has held true to her family's vow in the 1920s never to let the farm fall into the hands of developers, said she cannot fathom how she stands to benefit from either road project.

Banks said she is the last member in her family who would continue farming. In past decades she has evaded developers, and in the early 1960s, her farm and the Black Angus cattle residing there survived various plans for building federal offices and highway projects over the farmhouse and outbuildings built by her grandfather, Ignatius Beall Ward, the area's first postmaster.

Her supporters -- many of them Route 28 commuters -- have testified before transportation officials that they have come to appreciate the manicured green pastures, white fences and farmhouse on her farm as welcome relief from the stacks of suburban houses blanketing the surrounding hillsides.

Thomas M. Anderson, Banks' Rockville attorney and one of her former elementary school students, said that the recent assessment appears to be another county move to run Banks off her farm.

"It's terribly unfair," Anderson said. "All she wants to do is stay out there."

But Merryman said Banks' property was assessed as any property that fronts on the roads would be.

Assessments don't become official until after a project is complete -- this fall for Key West Avenue and 1988 for the Muddy Branch Road widening. The County Council then conducts assessment hearings to determine who benefits from the road improvements.

Though the county allows landowners to pay assessments over a 20-year period, Banks -- whose income consists of retirement benefits plus money she makes on the farm -- said that she would be forced to sell her farm to pay the costs.

But Banks said she has no plans to do so, and plans to fight the assessments.

"If I wanted to sell the farm, I could sell it tomorrow," Banks said. "But I don't want to sell the farm. The money doesn't mean that much to me. All I want is to be left in peace."

Legislative help may be on the way, however.

A bill sponsored by County Executive Charles W. Gilchrist, to be considered by the County Council's Finance Committee Monday, would allow farmers to defer road assessment payments for 20 years, and after that it would decrease the assessment itself over a second 20-year period. But the farmers would not be allowed to develop their property during that time; if they did, they would have to pay the assessment.