HAVING DISCOVERED that transportation is a top public concern throughout the region, the Greater Washington Board of Trade has come up with its own "agenda," one tipped in favor of the automobile. While there is no question that some new roads should be built and some old ones fixed, there is a danger in paving the way for more car traffic in the region. Too many times before, calls for a "balanced transportation policy" have ended up overemphasizing highways at the expense of mass transit. You're talking big money either way.

In September, the board of trade was talking balance a lot more carefully than it does in its latest report, which contends that highway construction has taken "a back seat" to expansion of the Metro transit system. That's debatable, but the board's recommendations would turn this around with a vengeance, at costs not even estimated in the report: It recommends 18 road projects, including the widening of all sorts of highways and the building of many new ones.

All of these may prove wonderfully popular with the taxpayers and may improve access to new development in the outlying counties. This assumes, of course, that all this development will prove just as desirable to the taxpaying residents whose neighborhoods it takes over. But the board of trade report contains a not-so-subtle suggestion that maybe the subway system will have to be shortened to provide more money for the roads: "While the Metro system is still an integral element of the transportation network, competition for federal dollars has raised serious concerns about the ability of the region to complete the 101-mile Metrorail system."

It's true that the dollars aren't coming easily, but it's also true that every public survey shows that people favor completion of the subway system as the region originally agreed to it -- and as people have been paying all along to see it through. To suggest that maybe some taxpayers will now have to be shortchanged and left without service is not consistent with the board of trade's past record of solid support for the 101-mile network.

The board also suggests that something other than a regional tax be found to support Metro. What it would be, other than cutting costs -- which is always a sound suggestion -- is not clear. A regional tax or some combination of taxes around the region dedicated to transportation (balanced, to be sure) still makes sense.