THE INTERESTING thing about Gov. George W. Bush's responses to Social Security questions on TV Sunday was not so much what he said as the fact that he felt free to say it. He suggested fundamental changes in the structure of the program. A few years ago, such remarks by a leading presidential candidate in either party would have been thought suicidal.

Even now the subject is tender. Bill Bradley was asked last month about raising the so-called normal retirement age at which an able-bodied worker becomes eligible for full benefits. It is already scheduled to rise from 65 to 67 over the next 20-odd years, and there has been talk of saving additional money by moving it to 70. Mr. Bradley had the temerity to suggest merely that the "discussion should continue."

For that, he was pounced upon by his ever vigilant rival, Vice President Gore, for wobbling on Social Security, and two weeks later felt constrained to say that while he favored further discussion he didn't think it was a good idea. No matter that Mr. Gore, like the president, has pusillanimously proposed nothing to strengthen Social Security's finances but to pay down debt, in part presumably to make it easier for future politicians to borrow again to cover the cost when baby boomers retire.

Mr. Bush has said he will "preserve Social Security." Asked how, he said he would let people invest part of their Social Security taxes in personal savings accounts to take advantage of growth in the stock market. At the same time, he promised to "keep the pledge to people . . . now dependent upon Social Security," which presumably means not cutting the benefits of those already in or near retirement.

The problem is that, the more you divert to personal savings accounts, the less you have to pay those benefits. To do the two at once would almost certainly require either additional revenues or eventual benefit cuts, as the governor himself half acknowledged. When then asked whether he would "look at" raising the retirement age as one possible cut, he said yes, but not right away.

Diverting a share of existing Social Security taxes to personal accounts seems to us a bad idea that would compound the problem it purports to solve. If savings accounts are thought to be a solution, they should be added to the program rather than carved out of existing revenues. Raising the retirement age is meanwhile merely one of several possible ways of reducing benefits, each of which needs to be weighed mainly in terms of its likely effect on the lowest-income beneficiaries. But right or wrong, Mr. Bush put the outline of a proposal on the table, as in varying degrees have most of the other Republican candidates. If the Democratic rivals agree that a problem exists, how would they solve it?