How major an issue is the savings and loan scandal in this political year 1990? Based upon the evidence of two reluctant U-turns publicly taken respectively (and unhappily) by the Republican in the White House and the Democrats on Capitol Hill, the answer is big-time major.

So enormous is the price tag for the S&L bailout that President Bush was forced to abandon his no-new-taxes oath, while to tranquilize the voters' rage at the scandal's cost and corruption, congressional Democrats warily voted to reform the rigged campaign-financing system, a system that has contributed enormously to reelecting incumbents and discouraging challengers.

The only question remaining about the S&L saga and the upcoming fall campaign is whether this scandal will be a principal issue or the principal issue on voters' minds.

Republicans, who stand to suffer most, can only pray for neither of the above. Recent national polls, following publicity about Neil Bush's "incredibly sweet deal" and his performance as director of the failed Silverado Savings and Loan, have given the president two-to-one negative scores on his handling of the S&L situation. By a similar two-to-one margin, voters blame the crisis-scandal on the Republicans rather than on the Democrats.

The political problem of the Republicans is that by 1992 they will have held the White House for 20 of the last 24 years -- and for all of the last 10. The iron rule of credit/blame in American politics holds that you can take bows for everything good -- the fall of the Berlin Wall, the collapse of the Soviet Union, economic good times -- that happens on your watch. The down side is what hurts. A hostage crisis, an oil embargo and government scandals leave the guy in charge with a political black eye and a fat lip.

The Republican defense of blaming everything on an omnipotent Democratic Congress is fatally flawed. That Ronald Reagan was a strong leader and a successful two-term president is almost universally stipulated. Now we are supposed to believe that the same Gipper who brought the Red Menace to its knees and to the negotiating table somehow trembled in the legislative company of defeated House banking chairman Fernand St Germain (D-R.I.). No, sir, that's not the Ronald Reagan we watched destroy the air traffic controllers union and tame a sullen Congress into doubling the defense budget and cutting taxes by a third.

This is not to suggest that all Democrats were innocent bystanders in this seamy story. They weren't. In every American town larger than a hamlet, the local banker has reliably been the Republican finance chairman for the business establishment. Democrats looking for a route into business checkbooks regularly recruited as their guide the local savings and loan chief, who was usually more nouveau and less establishment than the banker.

Congressional Democrats were far from unfriendly to the savings and loan interest, whose campaign contributions during the 1980s went to incumbents over challengers by a margin of 19 to one.

A shotgun marriage of liberal interventionism and conservative laissez faire contributed to the S&L disaster. In 1933, in every city in the nation were banks with closed doors. Millions of Americans lost their life savings. The Democrats' answer was to federally insure citizens' savings and to strictly regulate the financial institutions. Conservative Republicans put their faith instead in the market: if enough depositors wanted insurance on their savings, the banks would provide it at a competitive price. For Republicans, regulation was a euphemism for antibusiness, bureaucratic meddling.

What we got in the 1980s was the worst of both worlds. We, the taxpayers, guaranteed and insured all deposits while the Republican administration, the fervent disciples of deregulation, all but eliminated federal monitoring. It was a guaranteed formula for disaster. As the Democratic majority leader of the U.S. Senate, George Mitchell of Maine explains, "The Republicans wanted to get the government off our backs, but most especially off the back of anybody who owned an S&L."

For the recent Senate passage of authentic campaign finance reform, Sen. Mitchell deserves credit and co-billing with the S&L scandal. Recognition is also due to Sen. David Boren (D-Okla.), who began this battle seven years ago in a joint effort with the now retired Arizona conservative Barry Goldwater. The resistance of incumbents to any tampering with a divinely inspired system that keeps turnover to a minimum could only be shaken by a big scandal and an effective leader. Too many House Democrats who were fiery reformers in the '70s have become today's subcommittee chairmen and grumpy defenders of the status quo. What our politics desperately needs is competition. And in American business and politics, one's enthusiasm for competition is in inverse ratio to his percentage share of the market.

In 1990, the early returns already indicate that S&Ls are really big.