For months Virginia's two top Republicans, Gov. John N. Dalton and Sen. John W. Warner, have waged an intensive lobbying campaign to win $300 million in federal funds to improve the state's jammed coal piers.

Yesterday, at a Norfolk press conference to which only Democrats were invited, a top Carter administration official announced that the president plans to seek quick approval of the project, a move that Republicans denounced as a last-minute effort to shore up support for Carter's reelection in Virginia's largest, and traditionally Democratic, city.

Despite Republican grumbling that the announcement is a "pork barrel promise" that lacks any commitment of funds, officials of both parties cited it as just one example of an 11th-hour blitz by Democrats in Virginia, the only southern state Carter failed to carry in 1976.

"That [Norfolk] announcement will have no effect," predicted Bob Hausenfluck, coordinator for Republican Ronald Reagan's campaign in Virginia. "It's too little, too late. Besides it wasn't Ronald Reagan that took the Saratoga and Forrestal out of there," he said, referring to unhappiness over the decision to send the two Norfolk-based aircraft carriers to Philadelphia for overhauls rather than keeping them in Virginia shipyards.

A poll released yesterday by The Richmond-Times Dispatch tended to support Hausenfluck's opinion. It showed that Reagan holds a 12-point lead over Carter, a reversal of earlier polls that showed the president narrowly trailing Reagan in the state. The newspaper's telephone survey of 708 voters showed that 40 percent support Reagan, as compared with 28 percent who chose Carter. Six percent said they would vote for Independent John Anderson and the remainder were undecided or declined to disclose a preference.

"It doesn't faze me at all," Bill Albers, Carter-Mondale coordinator for Virginia, said of the poll. "They [Times-Dispatch] did the same thing in 1976; they showed that we were getting further behind when in fact we were getting closer.

One of the areas where Carter and Reagan forces are pushing hardest is in Northern Virginia, which four years ago provided 18,000 of the 23,000 votes that defeated Carter in the state. Earlier this week at a press conference at National Airport attended by the region's incumbent Democratic congressmen, another Transportation official released $210 million in previously promised constructed money for Metro.

The Carter campaign received a boost yesterday when the Baptist Ministers Conference of Northern Virginia, a group of 140 black ministers who claim congregations with a total of 25,000 members, broke a 40-year tradition of avoiding political stands and endorsed Carter.