The Virginia Electric and Power Co. asked yesterday for a temporary rate increase that, if granted in full, would raise customer's bills at least 13 percent and perhaps as much as 28 percent over what customers would pay under the current rate structure.

Vepco Vice President William W. Berry said at a press conference in Richmond that the increase between September and October electric bills would be 13.6 percent, under a proposal the company presented to the Virginia State Corporation Commission, (SCC).

The company claims the rate increase is necessary because the shutdown of two of its nuclear reactors forced reliance on more costly fuels to generate electricity.

Controversy quickly arose over the size of the increase because it would take effect in October, when lower winter electricity rates also begin. Berry said he computed the 13.6 percent increase by calculating the difference between $56.75, the amount of an average residential bill in September, and $64.47, the amount in October if the Vepco request is granted.

Vepco spokesman Dennis Hedgepeth said later that without the requested increase, customers would pay $50.39 in October. Using that figure, the increase would total 27.9 percent.

"I'd have to say their figures are suspect," said Del. Erwin S. Solomon (D-Hot Springs), an attorney representing the Virginia Consumers Congress.

"I don't know if they're playing with figures, but I don't figure it the way they do," he said.

The confusion over the percentages capped a day of controversy during which Vepco officials gave the SCC two proposals for recovering fuel costs and disputed figures The Washington Post reported Thursday.

Under both proposals made to the SCC, the company would receive an additional $91 million it says is necessary to make up higher fuel costs incurred during lengthy shutdowns of two of its nuclear reactors.

The first plan would allow Vepco to recover the entire $91 million during the last three months of 1979. That proposal would add $14.08 to the average monthly residential bill of 1,000 kilowatt hours.

The second and more complex alternative would spread the increase over a nine-month period, raising the average bill by $7.50 in October and November, reducing it to about $7.36 in December when the North Anna Two nuclear plant begins operation. The rate would be further reduced to $3.10 for the next six months of 1980.

Vepco Treasurer O. James Peterson III said he suspected the SCC would prefer the second plan because it would have less immediate financial impact on customers.

State Sen. Clive L. DuVal II (D-Fairfax) said, "under either plan, it's a huge amount" and two expensive. He said he plans to contest the company's projections at next month's SCC hearing.

Last month, Vepco President Stanley Ragone wrote the SCC'S three commissioners predicting the company would fall $131 million short in paying fuel expenses unless the agency granted a rate increase. He warned that if Vepco were prevented from collecting the money until the last three months of 1979, the increase would add about 40 percent to customers' bills.

In a telephone interview Monday, Ragone cited the 40 percent figure again, though he said he didn't believe the SCC would grant such a large increase.

On Wednesday, another Vepco official who asked not to be identified said that while the increase had not been finalized, it would be "somewhere between 30 and 40 percent," with the total dollar amount "in the neighborhood" of $130 million.

Ragone said yesterday that a Washington Post story citing the figures was "totally wrong." He said the $130 million referred to Vepco's fuel cost shortfall for its entire service area, which includes parts of North Carolina and West Virginia as well as Virginia. The SCC'S hearings will deal only with Virginia's share of the expense, which the company now puts at $91 million.

As for the percentages, Ragone said they had not been finally determined when he spoke to a reporter.

"I said I thought they would be high, but I didn't say how high," Ragone said.