Influential leaders of Virginia's black community, in a move that could further fracture the state's divided Democratic Party and harm Lt. Gov. Charles S. Robb's gubernatorial chances, today accused party officials of discriminating against blacks and violating the Voting Rights Act.

Virginia NAACP Executive Secretary Jack W. Gravely said his group was joining with party activist Paul Goldman in complaining to the Justice Department that the Democrats violated the federal act last month by adopting a delegate-selection plan that will give more power to predominately white suburbanites and less to traditionally black and Democratic urban dwellers.

Gravely said the party also violated the act, designed to protect the voting rights of minority groups in southern and western states with a history of discrimination, by not submitting the plan to the department before its adoption. The plan will govern selection of the delegates to a May convention in Virginia Beach that will sellect the party's nominees for governor, lieutenant governor and attorney general in fall elections.

In a letter to state party chairman Owen Pickett last week, the Justice Department's Civil Rights Division warned the party that it must submit the selection plan for review either by the department or to the federal district court in Washington. The plan cannot go into effect until approved, the letter noted.

Justice spokesman John Wilson said the party has "the burden of proof to convince either the court or the department that the convention system is not intended to discriminate or even that it has a discriminatory impact."

The NAACP's charges were supported by L. Douglas Wilder of Richmond, Virginia's only black state senator and leader of the black legislative caucus, who has called the authors of the delegate-selection plan "either ignorant or insensitive" to the state's black voters. Wilder predicted that divisions caused by the plan could hurt both Robb, the party's certain guvernatorial nominee, and other Democratic candidates in the November elections.

Pickett has denied that the plan is racially discriminatory had has accused Goldman, a political strategist who ran former Lt. Gov. Henry Howell's successful 1977 gubernatorial primary, of conducting a personal campaign against him. A conservative lawyer and legislative delegate from Virginia Beach, Pickett defeated a Howell-backed candidate for the chairman's post two months ago.

Other Democrats said they were concerned the allegations wouls weaken a party attempting to heal from more than a decade of major electoral defeats in time to recapture the Governor's Mansion this fall. "We've got an awful lot at stake this year and we want as many people happy as possible," said Robb political aide Laurie Naismith.

The "main target" is the GOP's certain gubernatorial nominee, State Attorney General J. Marshall Coleman, who won nearly one-third of the black vote in beating a conservative Democrat in 1977. Most observers believe Robb must recapture those black voters to break the GOP's 12-year gubernatorial win streak.

Blacks compose 19 percent of Virginia's population but only about 13 percent of the state's registered voters. Under the formula used at the Democratic Party's 1978 convention, localities were allocated delegates strictly on the basis of past Democratic vote totals, a system that gave cities with shrinking populations, but large black Democratic turnouts, an advantage.

Last month, the Democratic state central committee broke with tradition by voting to hold a convention instead of a gubernatorial primary. It also approved, in a close vote, allocating delegates by a formual that would give equal weight to local population totals.

Goldman contends conventions are inherently less democratic than primaries and his analysis indicates the new selection formula would cut the number of Democratic delegates from 11 major Virginia cities by nearly 10 percent. "This will definitely lessen black participation . . . . The party is not dealing in good faith with loyal Democrats," said Gravely.

Democratic leaders say they are holding a convention to save campaign money and limit bitterness between rival candidates. They say the purpose of the formula shift is not to exclude blacks, but to expand the party's base by bringing in more participants from growing suburban areas that in recent years have voted. Republican.

"As one of the committee members pointed out, the old method was fine in awarding Democratic voters but at the same time it hasn't won many statewide elections," said Naismith.

The party has 20 days to respond to the Justice Department's letter. Virginia Democratic Party executive director Russel Rosen said the party may argue that the Justice Department in effect approved the convention formual five years ago when it reviewed a long-range party porgram document that included a possible shift to gubernatorial conventions.