The controversy over extension of Interstate Rte. 66 from the Capital Beltway to the Potomac River has been going on so long now that new developments are beginning to sound like repeats of previous episodes. And sometimes they are.

In the latest tussle over his short but passion-inspiring strip of concrete, Virginia Gov. Mills E. Godwin has sent off yet another angry letter to the U.S. Labor Department concerning the department's insistence on sharply higher wage scales for construction workers building the Metro subway in the 1-66 median compared to workers on the highway portion.

It was only last spring that Virginia was able to persuade the Labor Department's wage appeals board to abolish the dual wage scales on the first 1 1/2 miles of the 1-66 extension now under construction.

The Labor Department has different wage scales for "heavy" construction work. As a result, those working on the Metrorail portion of the project would be paid more than double than those working on the highway portion, even though the kind of work they would be doing would be exactly the same.

Under the Labor Department guidelines, an unskilled worker laboring under the highway rate would earn $5 an hour for his efforts, while a few feet away, a person doing the same work on the Metrorail portion of the project would earn $9.56.

Despite the abolition of the dual scale on the 1 1/2 mile segment extending from the Beltway to Rte. 7 in Fairfax County, the Labor Department has reinstated it for another 1 1/2 mile segment extending from Rte. 7 to the Arlington County line. The reasone, accroding to a Labor Department spokesman, is that the second segment contains much more Metro-related construction work than the first.

In a letter dated Tuesday, Godwin called the Labor Department's decision "inflationary," "inequitable" and "absolute nonsense." Godwin also said that he was "astonished" that the department was sticking to a scale that he felt the wage appeals board had already overturned.

The Labor Department and the Virginia highway department also disagree on what to call a planned srtucture in the new 1-66 segment. That is at the heart of each side's argument on the pay scale issue.

It's a tunnel, the Labor Department says of a tube that will take Metro trains under the roadway and off to a service yard in East Falls Church. A tunnel, Labor officials said, menas heavy construction and heavy construction means separate pay scales.

"It's a concrete reinforced boxed culvert," according to Virginia transportation director John E. Harwood. "We build them all the time on high ways," Routine highway construction would not come under the heavy construction pay scale.

In his letter, Godwin has asked Labor Secretary Ray Marshall to "personally intervene" in the controversy. Harwood, meanwhile, has indefinitely postponed bids on the contract for the segment. According to Harwood, the state will go to court if the decision is not changed through Labor Department channels.

A Labor Department spokesman, however, said that the department thas not received Godwin's letter and thus could not comment on whether Marshall would intervene in the decision.

"I think we've been through this before," Harwood said.