THE HOME-BUILDING industry--backed first by key congressional Republicans who have now been joined by Senate Democrats--is knocking on the White House door looking for a handout. With housing sales and construction at postwar lows, the builders are looking for relief in the form of government-subsidized loans for new-home buyers.

Because the subsidies would be substantial--the government would pay up to four percentage points of mortgage interest owed by low- and moderate- income new-home buyers for five years under the Republican plan--it would add a billion dollars a year to the already large federal deficit. In the time- honored tradition of deficit spenders, congressional backers of the plan--who include Sens. Richard Lugar, Jake Garn and Mark Hatfield--argue that their plan will pay for itself because it will create jobs and boost tax revenues in the future.

That, of course, is an argument you've heard before from all the many promoters of this kind of tax cut or that kind of spending. If deficit spending paid for itself, by now the Treasury's coffers would be overflowing. And since money spent on new housing construction won't create any more jobs than money spent in dozens of other ways, you can also safely ignore the employment argument--unless you happen to be employed in the home-building industry. True, the housing industry is depressed, but what about automobiles and other credit-dependent industries? Shouldn't they get a special subsidy too?

What it boils down to is the question of how heavily the government should continue to susidize the housing industry. Easy credit and the negative interest rates produced by high inflation have, in themselves, made home ownership an unbeatable investment. Now the rules of the game have changed, and the home-builders are crying unfair.

In deciding how seriously to take their claim, you should remember that the biggest changes in the rules were produced not by the Reagan administration's specific cutbacks in construction and mortgage subsidies, but rather by market forces and larger shifts in economic policy. Housing demand is down not only because the economy is poor and interest is high, but also because the go-go psychology of housing investors pushed prices beyond reasonable bounds. Interest rates are up because lenders got tired of losing out to inflation and because there are important competing demands for credit.

Home ownership is an important value in American life, and people in this country have become accustomed to a level of housing far surpassing that generally available in Europe or Japan. But maintaining this high standard has contributed to the inflationary pressures of a high consumer credit economy and the relative neglect of investment in productive assets.