PRESIDENT CARTER has proposed a very big change in the way the federal government addresses the transportation problems of urban areas. If he prevails, the competition for federal funds between highways and mass-transit projects will be sharply reduced. And the states - along with the Department of Transportation - will have to start thinking about a coordinated surface-transportation policy, as distinct from separate policies for automobiles, buses and trains. The need for this shift has long been clear. Congress should get on with the changes the President seeks.

The awful proof of what fragmented Transportation planning has done to the cities is lying all over the nation. There are those spurs of the interstate highway system that go nowhere, such as the one off the Whitehurst Freeway at 26th Street. There are the mass-transit projects that have failed to live up to their expectations, such as San Franciso's BART. There are those states, such as Virginia, in which mass-transit proposals are neglected while highway proposals get priority treatment. In much of this, the federal government has been as guilty as state and local governments. That is because it has kept the financial balance tilted in favor of building highways for more than two decades.

Mr. Carter proposes to equalize the way in which federal funds are distributed so that local decisions are not influenced by the availability of federal money. The money would be there for either highways or mass transit - not, as it is now, in substantially larger amounts for highways. He also wants to make states consider the effect of their transportation plans on such matters as air quality, energy conservation and land use. If such proposal had been in place 20 years ago, the cities might not be nearly as uncomfortable places to live in as many of them are today.

We wish Mr. Carter had also proposed to eliminate the highway trust fund. The trust fund has distorted federal policy for years now, and its existence has made it hard to calculate what tax rate should be imposed on gasoline sales. Highways and mass-transit projects should be paid for out of general tax revenues, and the amount spent on them should have no relationship to the amount of money raised by particular taxes. Indeed, if an energy conservation program is successful in reducing the use of gasoline, the funds raised by current taxes may be inadequate to maintain the nation's highways - let alone to build more.

Congress should consider that possibility when it examines the revamping of transportation spending. It may then decide the time has come to let highways compete not only with mass transit but also with health, welfare, national defense and other programs for a share of the federal budget.