THE NATION'S bankrupt big steel companies have discovered a little faucet on the side of the Treasury. They turn it on and out comes money. The haphazard result is half an industrial policy. The government gives support to an ailing industry but without exacting any return, without imposing any plan or pressure on the industry to reform.

The device for this is an obscure federal agency called the Pension Benefit Guaranty Corp. It was created in 1974 as almost a footnote to legislation strengthening the private pension system. Premiums paid by healthy companies are used to make good on the pension promises of companies that fail.

The authors never imagined that whole industries might fail, as has happened recently with steel. Two large steel companies -- Wheeling-Pittsburgh and LTV -- have gone to bankruptcy and sloughed off their sizable pension obligations on the PBGC. Several competitors have threatened to do the same. The companies are using the PBGC as a kind of filling station, and now it is technically bankrupt too.

This unanticipated use of the bankruptcy laws presents an enormous policy problem. No one wants to strand the pensioners, and everyone wants the industry to survive. But no one wants to give the companies and those who invested in or lent to them a free ride, either. How to introduce greater discipline into the system?

The administration has proposed a premium increase (atop a small one already imposed in 1986) that would fall heaviest on companies with the least well-funded plans. As with auto insurance, those who pose the greatest danger would pay the highest charge. The problem is that those are also the companies that need to be nurtured the most.

Another proposal sometimes heard -- there are many -- is to move the pensioners farther up the claimants' line when a company files for bankruptcy. The pensioners would precede the bankers -- but then the bankers would be less willing to lend to suspect firms.

In all these proposals the basic choice between government support and government sternness is the same, but the choice is not being squarely faced. The pension insurance system has become a back-door way of aiding ailing industries, but the transformation has not been deliberate. The government is giving such aid without having developed a clear policy for doing so. The pension insurors, mainly concerned with the integrity of their fund, are not the right people to make such decisions. Congress and the administration, to the extent that it still has the energy to do so, should confront the issue directl