IN A RARE LAPSE of disunity, nearly all of Northern Virginia's delegates and state senators have joined hands in Richmond to cheer for Gov. John N. Dalton's proposed increase in the gasoline tax. Whether these disparate legislators can really sing in 27-part harmony long enough to get the tax approved in good form remains to be seen. But their 22-to-0 vote (one abstention and four absent) to press for enactment of Mr. Dalton's plan is an encouraging response to his bid to help the region as well as the rest of the state.

This is not rubber-stamping but back-scratching: the governor wants money for highway work and Northern Virginia needs dollars for its subway. Mr. Dalton has proposed a 4-cents-a-gallon increase in the gas tax that could address both fronts. What the Northern Virginia group should pursue now is some formal understanding about the money for subway construction.Without this provision, as Del. Warren E. Barry (R-Fairfax) said, the bill would not merit the delegation's support.

The importance of this bipartisan effort to people in Northern Virginia should not overshadow the benefits it would provide for people in other localities. The opportunity to do something about highway and mass transit projects at the same time should not be ignored by the delegates and state senators from any part of the state -- for the 4-cent solution is a sensible blend of revenues and regional interests.

There are some backstop measures being introduced by Northern Virginia lawmakers, including proposals for a regional sales tax or gas tax to help cover transit costs. In the past, varioius versions of these bills have been kicked around Richmond and this region without success. But right now there is the unusual situation in which the governor and the representatives of this region are agreed on a plan -- and that is where the legislative focus should be.