The Virginia Board of Education today effectively delayed for at least a year a Fairfax County proposal to divorce Fort Belvoir from the county school system, a move that may force Fairfax to absorb up to $4.4 million in cutbacks in federal aid for the children of military personnel.

Fairfax and York counties had asked the board to establish military bases as separate school districts in an attempt to counter anticipated cuts in so-called impact aid. The counties are hoping that such a move would force the state and federal governments to operate public schools in the new districts, relieving county taxpayers of the costs of educating thousands of military dependents.

The state board postponed a decision pending the outcome of Justice Department lawsuits against the counties attacking the constitutionality of the counties' plans to impose tuition on military students.

"At least they didn't reject the notion completely of separate school districts," said Thomas Cawley, attorney for the Fairfax board. "We still feel it's the responsibility of the federal government to educate these children."

The board ordered the state Department of Education to study the feasibility of the separate military districts, but set no deadlines for a staff recommendation. The board would have had to approve the measure before the opening of the 1982 session of the General Assembly in mid-January to implement the new districts by the opening of classes next year. The assembly has final veto power over the issue.

Some state education officials have expressed opposition to the plan because it could mean a substantial financial burden on the state government. Virginia bases its aid to local schools partially on the wealth and tax base of each district. A school district made up of military residents of federal installations, who pay no local property taxes, would presumably be entitled to large amounts of state aid.

Fairfax could lose much of the $4.4 million in federal impact aid it had been receiving for educating the 1,700 students at Fort Belvoir. Congress is still haggling over how the impact aid will be divided nationwide.

In another move, the state board rejected the toughest component of sweeping new regulations for teacher certification, after two years of study and controversy. The vote was a major defeat for S. John Davis, state superintendent and former head of the Fairfax County schools.

Davis had proposed giving teachers a two-year probationary certificate until they prove themselves in the classroom after college graduation. State teacher organizations bitterly fought the suggestion. Teachers will continue to receive certificates automatically upon graduation from a state-approved teacher education college.

Although the board rejected that proposal 5-to-4, it approved the rest of a package that imposes the most drastic changes in teacher certification in Virginia in more than a decade.

The biggest change requires colleges to upgrade admissions to teacher education programs. The admissions policies must be no less stringent than those of any other program at the university, including such traditionally tough areas as chemistry and other sciences.

The new regulations, which take effect in July, also require colleges to upgrade their faculties and tightens evaluations for student teachers.

"The vast majority of colleges in Virginia will have to make significant changes to meet these requirements," said one Education Department official who helped shape the new regulations.