The worst nightmare of senators preparing amendments to be offered when tax revision comes to the Senate floor is not that their proposals won't be accepted.

It's that they won't be first in line to offer them.

The peculiar politics of tax revision dictate that every amendment to restore a deduction -- and thus cut federal revenue -- must be accompanied by a proposal to raise the same amount of money elsewhere.

But only a limited number of tax increases are politically acceptable, and the amendment process is first come, first served.

"There's no doubt the order makes a big difference. If an amendment comes up, the chances are much better if it's offset by attacking a politically weak portion of the package," Max Baucus (D-Mont.) said yesterday.

William V. Roth Jr. (R-Del.), for example, is expected to propose repealing a tax break for defense contractors as part of his amendment to restore the full deduction for Individual Retirement Accounts. The committee bill would limit IRAs for all workers except those not covered by any other pension plan.

If Roth succeeds, that source of offsetting revenue would be denied to authors of subsequent amendments.

Rudy Boschwitz (R-Minn.) is looking at turning the personal exemption, which would increase to $2,000 under the bill, into a tax credit of $300.

That would provide the same benefit to lower-income taxpayers but give less relief to the wealthy. It would also help to pay for possible amendments to restore low tax rates on capital gains, ease the impact of an antitax shelter provision and restore the full IRA deduction.

Alfonse M. D'Amato (R-N.Y.), Christopher J. Dodd (D-Conn.), Alan Cranston (D-Calif.), Larry Pressler (R-S.D.) and Frank H. Murkowski (R-Alaska) said yesterday that they would propose keeping the IRA deduction and paying for it by delaying adjustment of tax brackets to compensate for inflation for one year.

"There will be a rush," said John H. Chafee (R-R.I.), a supporter of the bill as it is. "Who's going to be the first to push up the corporate rate? It looks like a very tempting thing."

Finance Committee Chairman Bob Packwood (R-Ore.) and his "core group" of six fellow senators are focusing on keeping the committee's package intact. The group yesterday discussed assembling a coalition committed to opposing all amendments.

Packwood, now in Oregon campaigning -- his primary is Tuesday -- is especially opposed to what he terms "killer amendments" that would alter the balance of tax cuts among various income groups. These include any changes in rates or brackets.

Parliamentarian Robert B. Dove said yesterday that Senate rules will help keep the plan "revenue-neutral" by requiring that costly amendments must be approved for consideration by a majority of senators before being debated.

The scramble is on to be first in line. Baucus said he is working on getting on the "A" list but wouldn't say how. "There's a lot of politics here," he said. "It's not always wise to divulge one's strategy."