ONE BY ONE, this region's suburban governments are glancing out the fiscal windows of their Metrobuses and wondering if this is where they get off to look for a cheaper bus system. Right now, they need look no farther than the driver's seat -- where sits a key figure in the high-number math of metro, whose labor negotiations are coming to a crucial head. April 30 is the date to circle in red, which is what Metro will be deeper into on the expiration of its already generous contract with the Amalgamated Transit Union that covers 4,000 drivers, train operators, station attendants and mechanics. Moderation on the part of the union has never been more critical of the future of the region's transportation net-work.

At issue is a clause in the current contract providing point-by-point protection against inflation -- pay increases every three months. If inflation increases 18 percent, so does a bus driver's salary. That is why all transit union employees just received an 18 percent increase -- which added $680,000 to Metro's budget deficit for the current year. It is also why local governments are flirting with proposals to start their own bus systems, even if such systems turn out to be more expensive or in conflict with labor protections Congress wrote into the Metro compact and federal transit aid laws.

Quite aside from the intricacies and inaccuracies of this kind of indexing, the arrangement enjoyed by Metro's employees could boomerang on the union if bus routes are discontinued and jobs are lost. As it stands, a fully experienced bus driver or train operator makes a minimum annually of $20,506, which is more than many teachers, firemen and police officers in the area. Without getting into who works harder or deserves more money, the guarantees now enjoyed by Metro's employees are a hefty cut above anything provided for any other public service employees in the region.

One can sympathize with the argument of the union over the years that its members should not be expected to absorb the costs of inflation just because they are public employees. But when so many others -- taxpayers and their governments -- are suffering these effects, the tears come a little harder. The more farsighted union leaders -- those who share the riders' hopes for a coordinated regional system even better than the one they now have -- should recognize the long-range benefits of some skillful moderation at the bargaining table in the coming weeks.