ANYONE WHO THINKS Metro's schedule of fares is complicated had best bone up on eight- dimensional algebra before trying to understand how and where it collects the rest of its money from participating governments. When we last looked, the formulas for computing various local, state and federal government shares of this region's mass transit system took into account almost everything from the number of miles traveled in each jurisdiction to the color of the last subway line to pass Go, or Metro Center, whichever comes first.

But the computations are not easily simplified, as Metro's various board members from around the region, as well as general manager Richard S. Page, can wearily attest; when you're dealing with two states, one District of Columbia, five counties, a Congress, a White House and a constituency of some 3 million people, the politico-logistics of fair-share membership can boggle the best of Metrominds.

Still, there are certain votes that can count more than others now and then, and one is that of the administration--which has the last word on federal funds--and which has just spoken about money for subway construction: Transportation Secretary Drew Lewis has cautioned that Metro could lose $100 million in construction money for the fiscal year beginning Oct. 1 unless Northern Virginia establishes a "stable and reliable" source of money by this summer to cover its share of Metro's operating subsidies.

"Stable and reliable" has become a familiar if vague phrase in Metro lingo, used by administrations and congresses to describe what they would like to see in the way of guaranteed revenue-raising efforts by each jurisdiction to meet its share of the transit money pot. And what Secretary Lewis is saying is that Northern Virginia's special tax on gasoline, which will rise from 2 percent to 4 percent this summmer, would cover too small a part of that area's subsidy bills.

Mr. Lewis seeks further assurances from state and local governments that the subsidies can be and will be paid. Sen. John W. Warner (R-Va.), who received this word in a letter from Mr. Lewis, has joined with other members of Virginia's congressional delegation is requesting help from Gov. John Dalton. Mr. Dalton's ability to assist is limited, of course, since he will be in office for only a few more days. But the next governor, Charles S. Robb, who already has voiced general support for Metro, should follow up by meeting with the Northern Virginia delegation to the General Assembly, whose members will surely need some support from Richmond.

Winning sympathy from other legislators around the state will take some doing, given their interest in roads rather than rails--and the fact that the state's highway fund is in sorry shape. Still, with strong and sensitive negotiating by the next governor and cohesion within Northern Virginia's delegation, there can--and should be--an effective coalition for a balanced transportation program that does not shortchange any section of Virginia.