RICHMOND, AUG. 20 -- A quarter million Virginia elementary and secondary school students may face a different set of standardized achievement tests next spring, under a proposal brought today to the state Board of Education.

The proposal by state Superintendent S. John Davis, which would also institute ability exams for first graders, would award a six-year contract for statewide testing to Houghton-Mifflin Publishing Co., ending two decades of testing by Science Research Associates. Houghton-Mifflin publishes a series of tests known as the Riverside Basic Skills Assessment Program.

State officials disclosed few details about the contract award, including the winning bid, because it has been challenged by one of the three losing bidders. The board discussed the contract award in closed session. Officials said they believe the challenge will not delay the board's scheduled vote on the tests next month.

The contract award comes amid growing emphasis on tests as a measure of school system performance. Virginia has required all fourth, eighth and 11th graders to take reading, math and language achievement tests every spring. It will add the first grade ability test this fall under a program designed to target "educationally deficient" school systems for improvements.

The state also will begin giving sixth graders a basic skills test, known as the "literacy passport," next spring. Two years later, students will be required to pass that test to enter high school. Virginia also requires that students pass a basic skills test in math and reading to graduate from high school.

Some school districts mandate additional tests. Fairfax County, for example, also requires second and sixth graders to take standardized achievement tests and administers tests in several additional subjects.

The test scores compare students in each school system with the national average. Despite the switch to a new test, 1987 scores can be compared to previous scores when different tests were used, state testing director Claude Sandy said. The winning test company was required to produce an equivalency scale to enable comparison.

No other Washington area jurisdictions use the Riverside series, and Houghton-Mifflin, citing the competitive nature of the testing business, would not release national sales figures.

The first impact of the new testing program would be seen in the fall, when the state will require first graders to take an ability test for the first time.

The first grade test scores are expected to have little impact in Northern Virginia, where students routinely score above the national and state averages. In Fairfax County, which tests students at the end of kindergarten to ensure they are ready to enter first grade, some officials believe the state requirement is needless.

"It's not going to serve any purpose for us right now," said Joseph Montecalvo, a testing specialist with the county schools. "We feel we have enough information already."

Students should find the Riverside tests used for later grades similar to the six-hour multiple-choice SRA tests they have taken in the past, Montecalvo said.

In other action, the state board approved six-year plans for special education for three dozen state school systems, including Fairfax County, despite an emotional speech by Marjorie deBlaay, founder of Parents for Compliance, which has been a vocal critic of the county's education of the handicapped.

The group had succeeded in persuading the board to postpone last month's scheduled approval of the plans, which are required for the local school systems to receive federal funding.

The board also received a tentative outline of a proposed state sex education curriculum that urges all school systems to teach students about acquired immune deficiency syndrome as early as the fifth grade. Many school systems do not offer lessons about AIDS until intermediate school.

The proposed curriculum must go to the state legislature for review and may be approved as a guideline rather than a requirement.