IN OUR DOG-EARED COPY of The Greater Washington Anthology of Seemingly Endless Planning Controversies-near the fat chapter called "The Tale of Three Sisters, and How They Grew"-there's an action-packed yarn under the title "I-66." It's the story of a Northern Virginia highway coridor between the Capital Beltway and the Theodore Roosevelt Bridge-and the nip-and-tuck, 20-year effort either to build or to block the freeway strip. We raise the subject one more time in light of a message this week from President Carter to Rep. Joseph L. Fisher (D-Va.). For the benefit of anyone. who may still be clinging to some hope of killing I-66, the word is . . . Give up.

The last gasp from the road's opponents was a series of protests that the state was building the right-of-way wider than necessary. The implication was that this was being done to permit a widening of the road to eight lanes someday when nobody's around to remember the agreement prohibiting this. At the urging of the Arlington County Board, Mr. Fisher sought an appointment with the president to raise this fear and to recheck Mr. Carter's feelings about I-66. Mr. Carter has now replied that he will not reopen the federal decision permitting Virginia to construct the four-lane highway.

Moreover, the president called Transportation Secretary Brock Adams on Wednesday and asked if the project was being closely monitored and built within terms of the agreement between the federal government and the state of Virginia. "I assured the president that it was," Mr. Adams said. He added that his department has been studying the I-66 design and construction practices and that "we have no reason to suspect it isn't being done precisely by the numbers."

We trust that the monitoring will go on until the work is done. But the fight is over. A deal's a deal: Name it the Mills Godwin Highway, in honor of the former governor who drove the I-66-for-Metro bargain that let the road be built and let officials get on with the business of financing and promoting mass transit-and doing whatever else it can to ease the daily traffic in this corridor.