CORPORATE EXECUTIVES and lawyers were busy last Friday putting the final touches on retroactive lease-a-tax-break deals. Those who missed the midnight deadline will have to wait until next year to take advantage of a new provision in the tax law that is likely to cost the Treasury nearly all of its corporate tax receipts in future years.

The idea behind the new provision was to let corporations without taxable profits sell their unused tax breaks to profitable companies. To qualify, the transaction must be disguised as a sale of property or equipment. The item sold is then leased back by the seller at a price that covers all costs of the sale less some part of the value of the tax breaks that go with the investment. In practice it's just a paper transaction in which a company gets some benefit from a tax break it can't claim by sharing the break with a more profitable company. You could call it "trickle-up."

This is a very expensive way to help out losing companies simply because much--perhaps most--of the benefit ends up in the hands of companies that are doing just fine. Because the market in tax breaks is so new, the price hasn't settled down yet--and it will always be volatile. But from what is known of the IBM- Ford deal, for instance, it looks as if Ford--the company in trouble--is getting only about 20 cents on the dollar for its tax breaks. IBM gets the rest.

The market in tax breaks is likely to be very large because a company needn't be unprofitable in order to have tax breaks to spare. Some, like Occidental Petroleum, may have large foreign earnings that are already exempt from the corporate tax. But as the very generous depreciation deductions phase in over the next few years, many other companies are likely to have deductions and credits far in excess of their tax liabilities. The tax-break market is already so large that investment bankers estimate that Treasury losses over the first 90 days of the provisions already exceed the losses that were estimated for the entire first year.

A less expensive way to help losing companies would be to rebate to them all or part of their unused tax credits directly. That, however, would bring into even sharper focus the question of whether the government should be running a welfare system for failing enterprises at all. Many companies find themselves in trouble because of shifting circumstances or their own mistakes. Sometimes--but not usually--a case can be made that the public interest would be served by propping a company up until it can get back on its feet. But that case should be thoroughly examined by Congress before a decision is made to use taxpayer money to subsidize an inefficient enterprise.

You could conclude from all this that the lease-a-tax-break law is an inefficient way to do something that the government shouldn't be doing at all--and you would be right.