Arlington County Board Chairman Stephen H. Detwiler, who lost his reelection bid last month, gave a farewell speech to the board yesterday, but few of his colleagues expected it to be his final valedictory.

Before a large audience that gave him a standing ovation, Detwiler touted what he called the accomplishments of the board during the four years when he and two other Republican-backed independents held the majority.

Detwiler, who is generally characterized as a moderate with a conservative bent on fiscal issues, lost last month to Democrat Mary Margaret Whipple, whose election will shift board control to the Democrats next month.

"I challenge the new majority to match the present majority's record," Detwiler declared in a written statement.

During his term, the 39-year-old Arlington native told the board, the real estate tax, now 98 cents per $100 assessed valuation, was lowered 32 percent. He also said the school system, criminal justice system and social service programs were strengthened and economic development around the Metro stations was increased. Vitality was restored to run-down commercial areas at the same time residential neighborhoods were preserved, Detwiler added.

County Democrats were less complimentary in their assessment of Detwiler's tenure, arguing that county taxes have risen despite real estate tax-rate cuts because of increased assessments. They also contend that board Republicans have too often caved in to developers' demands at the expense of the community. "It has been a very welcome environment for developers," said Democratic board member John G. Milliken recently.

"I would say he's been the businessman's representative on the board . . . ," Ellen M. Bozman, a Democratic-backed independent, said in an interview. " But he generally has been the first of the three Republicans to come out in support of human services."

A vice president of Continental Federal Savings & Loan Association, Detwiler still has at least two more board meetings to lead before his term ends. But speculation has already begun in both Republican and Democratic circles that he may run again for the board or some other office next year.

Majority board members Dorothy T. Grotos and Walter L. Frankland are up for reelection next fall, but said they have not yet decided whether to run. Detwiler said he is "very flattered" by citizens who have urged him to run for office again, and declined to rule out the possibility that he would run for the board if Grotos or Frankland did not.

"This is not the right time," Detwiler said. "I haven't made any decision one way or the other."