Virginians are getting a bit of a break on their electric and telephone bills, thanks to lower corporate income tax rates, and the phone bills are going to fall even further by the new year.

A spokesman for the State Corporation Commission said last week that he is not sure how much phone bills could go down.

Last year's revisions in the tax code are cutting the highest rate of corporate income tax from 46 percent to 34 percent, and state utility regulators have been cutting utility rates as a result.

"The state Corporation Commission has urged the electricity and phone companies to pass that on to the consumer," said Ken Schrad, a spokesman with the commission.

Savings to the average residential user have been about $2 or $3 per month counting electric bills and phone bills, but Schrad said from his Richmond office the savings on phone bills should be even greater in 1988. The commission this week told Virginia's five main phone companies to come up with rate reduction plans to take effect by Jan. 1.

This year, the five phone companies cut rates by a combined $24 million, he said, as an effort to accommodate part of the cut in corporate income tax.

Among the state's five big electric utilities, four have cut rates both because of lower taxes and because the SCC lowered their rates of return in response to such factors as lower interest rates. A rate case for Virginia Power was pending, Schrad said.

Average residential users would save $1.41 per month under a proposal by Appalachian Power Co., while average residential customers of Old Dominion are already saving $2.21 per month, Schrad said.

Phone bills are 35 cents to $1 per month lower under the first round of phone company rate cuts.

The five phone firms are C&P Telephone, of Richmond, with 2 million customers; Continental Telephone Co., of Mechanicsville, 300,000 customers; Central Telephone Co., of Charlottesville, 200,000 customers; United Inter-Mountain Telephone Co., of Bristol, Tenn., 75,000 customers; and General Telephone of the Southeast, of Bluefield, W.Va., 30,000 customers.

The five electric companies are Virginia Power, of Richmond, with 1.5 million customers; Appalachian Power Co., of Roanoke, 380,000 customers; Potomac Edison, of Hagerstown, Md., 60,000 customers; Old Dominion, of Norton, 26,000; and Delmarva, of Wilmington, Del., 16,000 customers.