Arlington schools got a report card the other day, and like those of its students, there was both good news and bad news. The school system gets A's in electives and graduation requirements but almost flunks out when it comes to teacher pay and computer studies.

The report is the work of a 14-member panel of county high school principals and curriculum specialists that compares the Arlington school system with the recommendations of the widely publicized report of the National Commission on Excellence in Education.

The national commission's report, warning of a "rising tide of mediocrity" in education, recommended increasing math, science, foreign language and computer-science requirements.

The Arlington school report says county schools generally compared favorably with the national commission's overall recommendations for required courses and programs in fine arts, vocational and business education and assuring proper grading and regular standardized testing. But major changes are needed in the length of the school day, computer studies and teacher pay.

Both documents are expected to influence decisions significantly in the schools this year.

"They have had an effect," school board Chairman Simone (Sim) J. Pace said earlier this week.

Indeed, both reports formed the centerpiece for a two-day workshop for school administrators and board members last week. When the school board set its work priorities for the coming year at a meeting Monday night, issues targeted in both reports--a longer school day, additional graduation requirements, a master teacher system and expanded computer studies--emerged as high on the board's list.

In Monday night's action, the five-member board set as a priority more vigorous implementing of affirmative-action policies and pledged to consider instituting some of the reports' recommendations as early as next year. But the signs of how the specific recommendations of both reports will affect Arlington education are already visible.

Most of them come from board Vice Chairman Claude H. Hilton. He recommended last week that the majority of a $1 million school appropriations surplus (largely the result of unspent employe health benefits and a refund from prepaid benefits payments) be set aside for improving teacher salaries at the lowest levels. The board last year clashed with teachers over pay raises.

The county report supports the commission's proposals for increasing entry-level pay for teachers, instituting a "career ladder" that distinguishes master-teachers from beginning instructors and putting teachers on an 11-month contract schedule.

Pace has already informally worked out a master-teacher system that he says would be based on performance, not longevity.

Increasing the school day from six to seven periods "is almost mandatory" if graduation requirements are increased, according to the county report. Most board members have indicated they agree with Hilton's support for adding a seventh period to the current school day.

Hilton also asked that $175,000 of the budget surplus be set aside for more computers in the schools. He says the board acknowledged the importance of computer education last winter when it budgeted nearly $250,000 for computer instruction and equipment. Still, even this is a turnaround for the board, which a year before had budgeted only $47,000 for computer studies.

Hilton has suggested that the board consider including basic computer instruction as a graduation requirement. So did both reports.

The county report compares Arlington schools with an "educational excellence checklist" included in the national commission report.

"We far exceed the checklist," says instructional services director William P. Young, who oversaw the report. "Arlington schools come out well. A lot of things the Arlington School Board had already done."

The board had approved additional math and science graduation requirements prior to the release of the commission report this spring but the county report said school officials could require even more math and science.

A survey of Arlington's 1983 high school graduates has made school officials even more confident about how they stack up against the commission's checklist.

While only 18 credits were required to graduate from Arlington schools this year, nearly 90 percent of the county's 193 graduates earned more than 20 credits, the county report noted.

Still, the national commission recommendations and staff suggestions based on them promise to be the yardstick by which Arlington educators are going to assess their own programs this year. The reports, Pace said, "tend to focus your thinking . . . .

"I think most of our students exceed the requirements recommended by the commission ," he said. "But I think we could do better."