The Virginia General Assembly today approved the state's participation in the 1988 "Super Southern" primaries and caucuses that supporters say will give the region more clout in choosing Democratic presidential nominees.

The action brings to nine the number of southern states that have formally endorsed the plan to hold primaries and caucuses early in March. In Maryland, a bill is awaiting Democratic Gov. Harry Hughes' expected signature. Five other states, including Louisiana next week, are expected to support the regional plan by early next year.

The Democrat-dominated Virginia legislature today dismissed bitter cries of partisan tyranny from outnumbered Republicans and gave final approval to the plan during a one-day veto session. The Assembly had approved a version of the legislation last month, but it was amended today at the request of Democratic Gov. Gerald L. Baliles.

Baliles said widespread support in the South for the plan "indicates the potential for significant influence in the next national election." Many southern Democrats, among them former governor Charles S. Robb, have said the primaries offer a chance to boost moderate and conservative presidential candidates who would move the national party toward a more centrist position to compete with Republicans.

Fairfax Republican Del. Vincent F. Callahan called the law unnecessary and said the state GOP expects to challenge the law in court. It is a "tyranny by the majority meddling in intraparty affairs," he said. The state Republican Party has a protracted delegate selection process that would be difficult to compress into the Democratic timetable.

Baliles and other Democrats rejected GOP complaints here that the legislation unfairly forces the Republicans to participate in a speeded caucus system, saying Republicans in other states support the mass of primaries and caucuses.

"It does have a political purpose, but it is not a partisan bill," said state Sen. James P. Jones (D-Washington).

He said the state GOP, whose legislators voted in a bloc against the measure today, fear it will strengthen the Democratic party in the South and give the Democrats a better chance of winning the White House.

The bill requires that parties in Virginia hold their principal mass meetings to select delegates for the presidential nominating process on the second Saturday in March. The original bill would have established a state nominating convention for that Saturday, but was changed today at Baliles' request to conform to Democratic National Committee rules. States holding primaries would hold them on March 8.

The Virginia caucuses would select delegates to a late-spring state convention, where the state would complete its delegate selection process for the Democratic National Convention. The early caucuses would give a clear indication of which presidential candidates had support, but would not be final until the state convention.

The Super Southern measure passed in the Senate 37 to 7 and by a margin of 58 to 38 in the House.

State Sen. Virgil H. Goode Jr. (D-Franklin) voted for the bill today but warned that the effort could backfire, with both liberal and far right candidates energizing supporters to win the contests rather than less controversial centrist candidates.

Sen. Edward M. Holland (D-Arlington) backed the proposal, saying the South politically "is changing literally before our eyes" and is moving into the forefront of national politics and prominence.

The states in addition to Virginia that have approved the Super Southern plan are Alabama, Georgia, Florida, Kentucky, Mississippi, Missouri, Oklahoma and Tennessee. Only West Virginia has rejected participating in the plan, according to the Southern Legislative Caucus of the Council of State Legislatures.

In addition to Maryland, where favorable action is expected, North Carolina takes up the issue in June while Arkansas and Texas are to address the issue in sessions in January. No law is required in South Carolina, where party officials are said to favor the early date.

In 1984, the southern states accounted for about half the number of delegates needed for the Democratic nomination, party leaders said.

Political consultants say the early southern process -- only four states had early primaries in 1984 -- would force national candidates to give more attention to the South and perhaps switch to national television to compete in several regions of the country.

Skeptics of the plan also say presidential candidates still must compete in the first caucus in Iowa and New Hampshire primary, where media exposure and a victory could give candidates the advantage going into the southern contests.