Martin Feldstein, the Harvard economics professor who was chairman of President Reagan’s council of economic advisers, has excellent timing. So it was with interest that we saw that Mr. Feldstein’s National Bureau of Economic Research yesterday released a working paper by Mr. Feldstein on Social Security reform.

The paper examines the effect of replacing the current 12.4% “pay-as-you-go” tax with what Mr. Feldstein calls a “mixed plan” that has a 6.2% pay-as-yougo tax and 6.2% deposited into personal retirement accounts. Using Treasury Inflation-Protected Securities, or a combination of puts and calls known as a collar, it is possible to reduce the risk that the private accounts will lose money. The risk can be reduced so much that Mr. Feldstein refers to it as a “No Lose” plan.

In that context, Mr. Bush’s suggestion in last night’s speech of “eventually permitting all workers to set aside 4 percentage points of their payroll taxes in their ac counts” seems timid. That’s especially so considering that it is but an opening offer that will inevitably be whittled down further in negotiations with a Congress that has plenty of Democrats who are steadfastly opposed to any use of the payroll tax for private accounts. Will Mr. Bush be able to articulate why, if it makes sense to put 4% of a wage into a private account, it does not make sense to put 6.2% of a wage into a private account? Especially when Mr. Feldstein says that it is possible to do it with a “no lose” guarantee?

The Cato Institute, in its reaction to the president’s speech, also called for giving workers control of 6.2%, saying that the president’s proposal “doesn’t go far enough, fast enough.” Our own sense is that the Republican Party is still at an early stage in sorting the Social Security issue out. Mr. Bush is being bold by taking on the issue and by arguing for private accounts. But the details matter, and Mr. Bush would be wise to resist the urge to compromise too soon.