A fierce taxpayers' protest over sharply higher property assessments in Western Loudoun County appears certain to have one ironic result - higher costs for the county government.

County Commissioner of Revenue Lee T. Keyes, who doubles as tax assesor for $500 a year, notified the County Board of Supervisors on Monday that he wanted $25,000 in back compensation for services dating from 1972.

Keyes, angry over criticism that followed assessment increases averaging 16 percent and going as high as 100 percent, also sent the board a separate letter insisting on higher pay for the five assessors in his office whose salaries now range from $8,676 to $15,576.

He asked for an additional $17.560 annually to raise salaries in his office to a range of $11,076 to $18,033.

Keyes wrote, "They (his staff) and myself have been made to feel as if we were foreign agents bent on the destruction of the county."

He said later in an interview, "Without this sort of compensation I will simply drop this." As an elected, constitutionally authorized official, Keyes is not required to act as assessor.

The western part of the county, which was last reassessed on 1974 land values, was jolted when this year's assessments arrived.

Keyes' office was deluged with complaints, about 5,000 residents signed a petition calling for spending cuts and the County Board authorized an adhoc committee to investigate the assessment process.

That committee will recommend that assessment powers be taken from Keyes' office and placed under the county supervisors, according to Supervisor James F. Brownell.

Keyes said that the committee found that a shift to the county administration would require more presonnel than now used. Board members acknowledged that the cost would rise if the shift were made.

Keyes, in a third letter to the board, cited the ad hoc committee's conclusion that the latest assessment was "the best ever" in the county and defended his office's performance. He said that about 80 percent of assessments were "right on the money," that about 10 percent were too low adn about 10 percent were too high.

Keyes said that the eastern end of the county has been "overassessed since 1971 compared to the western end."

The eastern end was reassessed in 1977 and again this year, with a 1978 increase averaging about 5 percent, Keyes said.

He said the rural western part of the county, last assessed on 1974 values, has been undervalued for tax purposes until this year's reassessment. Keyes said that old houses, which often belong to people of wealth and political clout, have been particularly undervalued.

Supervisor Frank Raflo, who defended Keyes' preformance, said that Keyes had no choice but to raise assessments sharply in the west to real market value, but that "when a property owner gets a 60 percent to 100 percent increase, no explanation is satisfactory."