The Fairfax County Board of Supervisors has given its unanimous approval to a charter form of government for the county. But the document, which must go before the General Assembly before it can be considered by county voters at a referendum, may not be dealt with in Richmond for another year or more.

State Sen. Joseph V. Gartlan, Jr. (D-Fairfax), who headed the legislative committee that drew up the draft charter endorsed by the supervisors at their meeting Monday, said, "I anticipate the charter will be introduced at the forthcoming session of the General Assembly. But the consensus of the Northern Virginia delegation is that it will be held over for the following year (1979)."

Under the charter endorsed by the supervisors, Fairfax would be immune to any annexation attempt by a city. In the past, Alexandria has sought to annex contiguous portions of Fairfax, and while there is currently a ten-year statewide moratorium on annexations, legislators have said they will reopen the issue during the next session of the General Assembly.

On the subject of the powers of existing towns, the charter preserves the status quo. The document does not deal specifically with the controversial issue of creation of new towns. By avoiding that issue, the charter leaves any alterations in the present arrangements to specific state legislation.

Such legislation is expected to be a major issue at the General Assembly when it convenes in January.

The charter also would spell out Fairfax's powers more specifically than they are listed under its present urban county form of government, which is simply general state law applying to all urban counties in Virginia.In short, with a charter, Fairfax would have more individual identity, much like cities and towns.

But as Sen. Gartlan says, "If the charter is adopted, the sky will not look any different after the average citizen of Fairfax wakes up in the morning."

Early action on the charter in the General Assembly is not expected because the legislators will be contending with a whole packet of bills on related questions, such as annexation. Gartlan says that because the issues are so intertwined, it will take time to deal with them - more than one session of the General Assembly.

Under the proposed charter, Fairfax would be administered by a county manager instead of a county executive. The manager would be able to appoint and dismiss his department heads - powers now held by the Board of Supervisors. Critics of the present form of government say that the county executive is too hamstrung and that the supervisors because of their far-reaching authority, can meddle in what should be administrative functions.

The charter also states that the county, with approval of the voters, could issue bonds without going to the electorate for each separate issue.

The charter would also broaden the county's taxing powers by removing the ceiling on some minor levies, such as those on hotel and motel rooms. But already, under an urban county form of government, Fairfax can raise its real estate and othe major taxes with a free hand.