The Social Security trust fund is running a surplus. And as long as there is any excess money in the fund, Congress will continue to find a way to borrow and spend it.

For that reason it seems reasonable to make some cuts in the Social Security payroll tax that Americans pay. Putting the tax on a pay-as-you-go basis and eliminating any surpluses would end the practice of lawmakers leaving IOUs in the fund to pay for other programs.Borrowing to pay expenses connected with the war in the Middle East or other government operations shouldn't be permitted. It may give the appearance of making the government's mounting deficit look smaller. But any money borrowed must be paid back, and the federal deficit is just compounded.

Last October, the Senate killed a proposed cut in Social Security taxes after a warning that the reduction would deny the national treasury more than $150 billion and virtually kill any budget amendment.

Yet what happens when those hundreds of billions that were borrowed from the fund are needed in the future by Social Security?

For example, when the $150 billion borrowed in 1990 is needed some year to pay Social Security benefits, Congress will be caught in a double bind. It will no longer have any Social Security surplus to borrow, thus causing a gaping hole in available revenue. At the same time, it will have to find $150 billion somewhere to pay back to the trust fund.

As Congressional Quarterly points out, the Social Security payroll tax is one tax that Congress could cut this year without having to pay for it. But, the publication advises, "be forewarned . . . that somehow, somebody always pays."

In other words, Congress has gotten so used to borrowing Social Security surpluses that it can't live without them. If the surplus is taken away, Congress could very well take action to make up the difference. That certainly has some scary implications for most tax-conscious Americans.

Congressional Quarterly says that among those who might pay "could be the rich, if Democrats carry through on threats to raise payroll taxes to offset rate reductions for the middle and lower classes. It could be businesses, if workers get a Social Security tax cut but employers do not."

The Social Security tax cut is being sponsored by Daniel P. Moynihan, D-N.Y. His bill would abolish scheduled increases in the payroll tax, collected at a flat rate of 6.2 percent on all income up to $53,400, a rate matched by employers.

The tax would drop gradually over the next five years, stopping at 5.2 percent by 1996. Wages subject to the tax would climb to $82,200.

A lobbyist for the National Federation of Independent Business has termed the Social Security tax as the most "obnoxious and regressive tax" that its membership must pay.

Whatever is decided about the Social Security trust fund surplus, Congress should remember that countless Americans now rely and will have to rely on stability of the program in the future.

Nothing should be done that would endanger the stability of the fund in the future. Instead of giving Congress the opportunity to spend all the Social Security surplus now - and being faced with having to pay it back later when there is no surplus - it makes more sense to reduce the Social Security tax now and then increase it later as the need arises.