Virginia Electric & Power Co. directors voted yesterday to increase the utility dividend to common stockholders by 6 percent even though the utility has had problems with nuclear generating plants and is projecting a shortfall in revenues this year.

In a separate action, Washington Gas Light Co. asked the D.C. Public Service Commission to approve an interim, across-the-board rate hike of about 6 percent to bring in $6.1 million of new revenue annually.

In New York, meanwhile, an energy consulting company reported that electricity rates for large customers in the U.S. rose 7 1/2 percent from December 1977 to March of this year-lower than rate increases in such other industrial nations as Australia, Italy, France, South Africa and Britain.

But National Utility Service Inc. also warned that because of natural gas deregulation and the prospect of oil price deregulation, the U.S. can look for the "resumption of spiraling electric rate increases in the near future."

Vepco's directors voted a new payout of 35 cents a share on common stock, up from 33 cents previously, to be paid June 20 to owners of record May 31. Regular dividends on preferred and preference shares also were declared.

The decision marked Vepco's third dividend boost since 1973. Chairman T. Justin Moore Jr. said he hopes the higher payout "will make our common stock more attractive to investors who must provide a significant portion of the funds required to meet the needs of customers . . ."

Although it was Vepco's second consecutive yearly dividend increase, Moore noted that "it does not keep pace with the inflation rate."

Earlier this week, Vepco told the State Corporation Commission that the utility requires a 5.8 percent rate boost because projected revenues this year will be $64 million below premitted levels of earnings.

The dividend boost came as something of a surprise because Vepco's earnings per share declined to $1.77 in the 12 months ended March 31 from $2.00 in the same period a year earlier. Moore told the annual meeting last month there would be no immediate payout boost because of the earnings situation.

Washington Gas, which also has been reporting sagging profits, said yesterday's request for a temporary rate boost will be followed in about 45 days with a new permanent rate increase case. Any temporary rate hikes would be subject to refunds if the PSC subsequently ruled that lower charges were in order.

The Washington natural gas distributor asked the PSC to make the higher rages effective no later than Oct. 1. The across-the-board revenue increases being sought would add about $2.75 to the monthly bill of a residential heating customer and 60 cents to the bills of non-heating customers, WGI, spokesman Paul Young said.

Current and anticipated earnings resulting from the most recent D.C. rate case "won't enable WGL to finance construction necessary to provide expected levels of service," the company warned yesterday. Last year, WGL's rate of profit on its investment in D.C. service was 3.7 percent compared with an authorized return of 9.25 percent.

Earlier this year, the D.C. regulatory agency approved a $7.1 million annual rate, boost, some 20 months after higher rates had ben asked. At the time, WGL said the new rates were "too little, too late," since they were based on 1977 costs.