AFTER A BREATH-TAKING NON-FLURRY of eleventh-hour activity, the lawmakers in Richmond have gone home - leaving in their wake an impressive toll of dead bills. Nevertheless, even though General Assembly scorekeepers and other observers of these annual sessions tend to grade them on the number of "major" bills that were enacted, a case can be made now and then for a tame session in which relatively few legislative horrors are perpetrated.

One of the legislature's worst failures, in our view, was the rejection of a bill that would have permitted Northern Virginia to enact a sales tax to help pay for the Metro system. The disappointment was all the more bitter in that the House was but a single vote short of the number needed to pass the measure. While the impressive support was a tribute to some earnest lobbying by members of the Northern Virginia delegation - as well as by Fairfax County supervisors Marie B. Travesky and John P. Shacochis - the death of this proposal is a serious blow to efforts for some form of dependable Metro tax or taxes throughout the jurisdictions of Greater Washington. While it might not have swung the vote the other way, a word of support from Gov. john N. Dalton for the tax bill certainly wouldn't have hurt; instead, the governor stayed silent, apparently still opposed to any local tinkering with uniform statewide taxes.

Perhaps Gov. Dalton is content to see pressures continue on property taxes in Northern Virginia, but we suspect that more and more localities throughout the state will be seeking relief in the sessions to come. That surely accounted in some measure for the closeness of this vote. In the meantime, unfortunately, a fallback measure that would have raised some money for Metro through a regional increase in the gasoline tax also failed.

On balance, however, Northern Virginia fared better than it has in the past in terms of the budget. There were approvals of $10 million in construction money for Metro, as well as additional funds for higher education, schools, mental-health facilities and the corrections department. And, though it took some doing, Fairfax and Loudoun counties were able to rescue their beverage-container-deposit ordinances from special-interest legislation pushed through by the can-and-bottle lobby. Other counties and cities, however, would be banned from taking any local initiative to control the tons of throwaway metal and glass that are marketed and jettisioned each year in the state.

In failing to approve other important legislation - be it the Equal Rights Amendment, annexation, aid for abortions for indigent women or improvements in the regulation of utilities - the assembly certainly has left the makings of a full agenda for the 1979 session. One can hope that, by then, Gov. Dalton will be able to contribute some constructivethinking and leadership to the process in Richmond.