YOU CAN ASSUME that just about 99 percent of the people who travel by air are in favor of spending money faster to improve the system's efficiency and safety. They are right about that. But knocking loopholes in the budget rules will do little to help -- and can do a lot of harm.

The Airport and Airways Trust Fund, fed chiefly by taxes on airline tickets, currently has an accumulated surplus of some $5.6 billion. To accelerate the spend-out, the House Public Works Committee wants to take the trust fund out of the federal budget altogether and exempt it from the budget's restrictions. That won't work. Budget restrictions aren't the major constraints on outlays for the air travel system. The Public Works Committee is responding to the accusations that the administration -- with the help of congressional appropriations and budget committees -- has been deliberately cutting the money for air safety to hold down the federal deficit. But that's not the real explanation for the surplus. Most of it is for large capital expenditures, such as bigger computers and more sophisticated radars, that the air traffic control system now needs. Development of this equipment is running behind schedule, and the fund is holding the money until the hardware is ready. Meanwhile a lot of general tax revenue is being poured into air safety to meet needs that the trust fund doesn't cover.

Taking the trust fund out of the budget would exempt it from the kind of across-the-board spending cuts that the Gramm-Rudman-Hollings Act might eventually require. But it won't accelerate the production of the new radars.

One thing it would do very effectively is to set a deeply damaging precedent for taking one class of expenditures out of the budget's reach on grounds that they are too important to be subjected to any fiscal restrictions. It's true that air safety is essential. How about highway safety? Far more people are killed on the road than in airplanes. How about AIDS research? Or toxic waste cleanups?

As Congress refines its budget process and tightens up on the deficit, many committees can bring to mind special responsibilities that they think deserve exemption. But the whole point of the budget process is to force hard choices rationally. Exemptions such as the one now being pushed for this trust fund threaten to unravel the discipline of weighing each outlay against the others. It's a threat to Congress' control over its own purse. If this exemption is passed, President Reagan would be well justified in vetoing it