A CURIOUS THING has happened to the Highway Trust Fund. Once the target of those who thought too much money was being spent on highways, it now appears to be the target of those who want to spend even more. The bill approved by the House Public Works Committee to extend the life of the fund for another six years seems designed to kill it by spending it into bankruptcy.

The bill is the result of the committee's decision that $66.4 billion ought tobe spent on highways and mass transit in the next four years, with 45 billion of that to come out of the trust fund. Unfortunately, the Treasury Department estimates that the fund will produce only about $36.6 billion in that time. To get around the problem, the committee decided to authorize the fund to spend in four years all the money it is expected to raise in six. That is called anticipatory financing in some circles, but it sounds like deficit spending and bankruptcy to us.

There were two straighforward courses the committee could have taken if it really believed that the spending level it want is justified. One would have been to recommended an increases of 2 or 3 cents a gallon in the gasoline tax. The other would have been to recommend that the fund be abolished and the highway and other transportation projects it now pays for be financed out of general revenues. Neither is palatable to the highway lobby, so the committee fell back on the old gimmick of spending money that doesn't exist.

Part of the problem the committee wanted to solve was created by the trust fund. Its system of matching contributions has encouraged the states for 20 years to pour money into completion of the interstate system at the expense of maintaing highways already built. The result is a huge backlog of repairs and a highway network that is rapidly deteriorating. That situation should have encouraged the Public Works Committee to adopt the substantive changes in the trust-fund program sought by the Carter administration. Instead, it simply decided to raise the ante and maintain the status quo.

Fortunately, the bill approved by the committee must also clear the Ways and Means Committee before it reaches the House floor. Two committee members, Reps. Sam Gibbons (D-Fla.) and Barber Conable (R-N-Y.), are attempting to amend the bill so that the trust fund can't spend more than it receives in any year. Their amendment should be adopted - unless the full House is prepared either to raise the gas tax or simply abolish the trust fund.