The biggest change marking Manassas's 1990-91 school year will be hard to miss. It's the $13.3 million, 210,000-square-foot Grace E. Metz Junior High School.

As part of their orientation last week, Metz students got sneak previews of the school for seventh- through ninth-graders located at Richmond and Fairview avenues. It includes a 980-seat auditorium, computer equipped vocational education facilities and mobile language laboratories.

The students "were amazed, truly amazed," said Metz Principal Ann Yeck, who was principal at Jennie Dean Middle School for seventh- and eighth-graders. The sprawling new school is so big, Yeck said, she is proposing letting senior citizens walk the halls for exercise, just as they do in large malls.

When the new school opens its doors Tuesday, it will mean more space in schools throughout the system, which expects nearly 4,800 students this school year.

Preparing for 1,051 students, Metz will take the seventh and eighth grade from Jennie Dean, which has been expanded and converted into the city's fifth elementary school. "We have 10 brand new classrooms," said Jennie Dean Principal Diane Lottier, who was an assistant principal at Weems Elementary for seven years. "But even the old classrooms look brand new."

Metz also will relieve the city's only high school, Osbourn, of the freshman class.

Almost full last year with 1,150 students, Osbourn will have "a little bit of room to breathe now," said Superintendent of Schools James E. Upperman. It expects 850 students.

According to Upperman, the openings will let the entire city breathe slightly easier because the economic slowdown and cutback in state revenue is likely to mean less revenue for the city schools.

Earlier this month, Gov. L. Douglas Wilder proposed cutting a total of $173 million in state aid to school systems throughout the state to help offset a projected $1.4 billion budget deficit by July 1993.

Upperman said Manassas may lose additional state funding because the schools' enrollment has fallen 200 students short of the projected enrollment. State aid is based partially on the number of students in a jurisdiction.

"This is quite a challenge for us," Upperman said, explaining that the schools' current $31.4 million budget for fiscal 1991 provides only a 7 percent increase in spending over last year. "But we are fortunate in one respect: We have our buildings basically set." Other jurisdictions, he said, are starting to consider year-round school as an option to building new facilities.

While students may notice more space in their buildings, their classrooms will be more crowded than last year as a result of efforts to set up a $1.2 million reserve fund.

Upperman has frozen the hiring of 13 teachers needed in schools throughout the system, which will mean most classes will have a few extra students. For instance, a class that had 21 students last year may have 24 this year, Upperman said.

In total, the hiring of nearly 28 full- and part-time teaching and other staff positions is on hold as well as $180,000 in spending on items such as office equipment. In addition, Upperman has targeted 10 to 20 percent reductions in other areas of the schools' budget.

Because of the budget squeeze, new programs will be few, Upperman said.

The only major change, a non-letter grading system of assessing students' academic achievement, will be implemented in the first and second grades. Under the new system, students' progress in the classroom will be graded as satisfactory or unsatisfactory.

Psychologically, letter grades can be counterproductive, according Associate Superintendent for Instruction Thomas G. Bentson. For instance, a second-grader who receives a "C" in reading may conclude "I'm not a good reader and I hate reading," shutting the books mentally on reading forever, Bentson.

Non-lettering grading system "concentrates on learning instead of grading," Bentson said.

Bentson, who spent last year reviewing test scores and the schools' grading system, will be studying possible changes in higher grades during the school year.

The following are a few of the new or expanded programs that also survived the fiscal pinch: A pilot breakfast program at Jennie Dean. Expansion of the federally funded remedial math and reading program, called Chapter 1, from Baldwin Elementary to Dean and George C. Round elementary schools. A Center for Cultural Exchange at Jennie Dean for students as well as the general public, which will provide Spanish and Vietnamese translations of information on school and city services.

In addition, a citizens and staff committee is pulling together an agenda for the entire decade to present to the School Board.