The Justice Department rejected another Virginia redistricting plan yesterday, holding that the proposed realignment of the state's 100-member House of Delegates discrminated against black voters in the city of Petersburg and five nearby predominantly black counties.

The rejection of the House plan, which follows Justice's veto of a Virginia Senate reapportionment plan four weeks ago, threatens to disrupt scheduled Sept. 8 primaries for many of the House seats and could delay geneeral elections now set for Nov. 3 for all the seats.

"We are aware that there is a severe time problem if the commomwealth is to hold timely elections for the General Assembly," William Bradford Reynolds, an assistant attorney general, told Virginia officials in a letter rejecting the plan. But Reynolds noted: "I am unable to conclude . . . that the submitted plan . . . is free of any racially discriminatory purpose or effect in the described area."

Virginia legislative leaders said yesterday they could not assess what effect the ruling will have on the elections and if they can be staged as planned. "It's hard to tell," said House Majority Leader Thomas Moss (D-Norfolk). "I kind of feel like I'm going up a hill and I don't know what's onthe other side."

Virginia is one of 22 states required under the 1965 Voting Rights Act to submit all changes in election districts for Justice review to ensure fair treatment of minorities.It was under that act that the department acted yesterday.

"We're delighted . . ." said Chan Kendrick, director of Virginia's American Civil Liberties Union, which is one of 10 parties challenging the House plan in a federal court. "We felt there was clear dilution to black voting strength in those localities."

One of the localities cited by Justice is Petersburg, a city with a predominatly black population, which was combined in the rejected plan with the virtually all-white city of Colonial Heights. The resulting district would have been 43 percent black.

The other objection by Justice was to dissolving a district that had included four rural counties with black majorities. Under the proposed plan, each of those counties and a fifth predominatly black county would be combined with predominatly white counties, leaving blacks in a minority.

Justice did not address argument that civil liberties groups have raised in the court case that population variances between districts in the new plan are so great that they violate the Constitution's equal representation requirements.

"By and large [the Justice opinion] vindicates our work," said House leader Moss yesterday. "There wre only six areas of the state where they found any problems . . . If we can limit this problem within those six confined areas, then we could probably go ahead with the elections. But if we get into domino situation, then I can't really say."

Gov. John N. Dalton was more pessimistic that the legislative elections could be held on time. "You can't just pick out a little area of the state and say you're going to change just that" without affecting other areas, he said.

Most of the General Assembly's Democratic leadership had recently pushed to keep the 1971 district plan in place for the coming elections, arguing that the legal tangle was too complicated to sort out before the scheduled primaries.

But officials in Fairfax County and Virginia Beach, which gained additional representation as a result of the 1980 Census, on which the new plan is based, argued against that course of action. They charged that strategy was designed to save the seats of incumbents in areas losing populaton, such as Norfolk, at the expense of rapidly growing localities.

"I assume that this means we can't have an election under the present redistricting plan," said Democratic Del. Elise Heinz, whose Arlington-Alexandria district was abolished under the new plan because of population losses in the suburbs closer to Washington. Heinz had been one of the loudest critics of the new plan during bitter infighting over reapportionment during a special legislative session this spring.

"We all knew at the time that we were diluting the black vote. We didn't discuss it. We didn't do it on purpose. But there was no doubt that that was the effect," siad Heinz.

Virginia can request the U.S. attorney general to reconsider his objection to the plan, appeal it s case to the U.S. District Court for the District of Columbia or alter the plan to satisfy the objections of Justice. dLegislative leaders siad they expect to meet soon, perhaps next week, to consider what they should do over the issue.

The next scheduled meeting of the General Assembly is not until Sept. 10.