Gov. John Dalton announced today that George M. Walters, a former top executive of the Reynolds Metals Co., will succeed Wayne Whitham as secretary of transportation next month.

The appointment was seen by some observers as benefiting Northern Virginia, although the post of transportation secretary, which carries cabinet rank, has frequently less influence over transportation policy than the state highway commissioner, a position under the secretary's office.

John T. Hazel, a Fairfax lawyer who specializes in transportation and zoning, called Walters' selection "a very encouraging prospect for Northern Virginia."

A state official who declined to be named also cited Dalton's search outside Virginia's traditional highway establishment for a successor to Whitham as significant for Northern Virginians. "He's gone for a professional manager," the official said.

Whitham, who has serious heart problems, will resign effective Dec. 31, the governor said at a press conference.

Walters, 59, who retired early as vice chairman of Richmond-based Reynolds Metals last June, has also served as the company's president. Before joining Reynolds in 1965, he was a partner in Ernst & Ernst, an internationally recognized accounting firm base in Cleveland.

He is expected to consider Virginia's transportation problems without the regional bias that some Northern Virginians say has cost them a fair share of the state's transportation expenditures. With more than 20 percent of the state's traffic, the region has only about 8 percent of Virginia's state highway mileage.

Whitham was frequently outmaneuvered by his underlings, and efforts by a state management commission to strengthen the office of transportation secretary have been rejected by the legislature.

At the press conference, Dalton expressed satisfaction with his first year as governor, citing the state's anticipated $53 million budget surplus and a "healthy financila situation." But he said a major goal for next year will be to trim spending further. He offered no examples of where further cuts might be made, however, and declined to discuss next year's budget before its presentation next month to the legislature.

Dalton said he considers Lt. Gov. Charles S. Robb and Attorney General J. Marshall Coleman the apparent Democratic and Republican frontrunners, respectively, for the 1981 governor's race.

The governor's enthusiasm for Coleman, however, appeared lukewarm, especially when he announced that he met last week with Thomas T. Byrd, the Winchester newspaper publisher who is considered the political heir apparent to his father, Sen. Harry F. Byrd Jr. (Ind.-Va.).