Senate Finance Committee members last night adopted several minor amendments to their sweeping rewrite of the nation's tax code, with the most significant fights expected today.

Supporters of tax revision predicted the proposal would be approved by the 20-member panel, although few contended that the needed votes were solidly in line.

"When it's over, it's going to get a significant majority," Sen. Max Baucus (D-Mont.) said.

A few senators expressed misgivings about approving so quickly a package that would touch every taxpayer in the country, sweeping the poor off the tax rolls and savaging tax shelters for the rich.

It remained unclear whether Finance Committee Chairman Bob Packwood (R-Ore.) had the votes not only for final passage but to override attempts to restore popular deductions. But even the doubters said the tide seemed to be turning toward producing a bill.

"I'm not a 'yes' yet but I'm interested," said Sen. William L. Armstrong (R-Colo.), who opposed the committee's earlier effort to overhaul the tax code. When that initiative became overloaded with special-interest amendments and collapsed two weeks ago, Packwood took his panel behind closed doors to hammer out a cleaner bill.

The plan now before the committee would almost halve the top personal tax rate -- from 50 to 27 percent -- and reduce the corporate rate by nearly a third -- from 46 to 33 percent -- while wiping out numerous deductions and credits.

Changes made by the committee last night were relatively minor. In an indication that senators are willing to cooperate, all the amendments to restore deductions or credits were coupled with tax increases in other areas so that the final bill would not increase the federal deficit.

For example, Sen. Spark M. Matsunaga (D-Hawaii) proposed using $300 million "left over" from an amendment by Sen. Russell B. Long (D-La.) to help "pay for" restoring tax credits for solar and geothermal energy for one year, and the panel agreed.

However, several senators said they were saving their amendments -- most of which would take away federal revenue -- for when the proposal moves to the Senate.

Several big-ticket amendments are expected today, including proposals to restore the deduction for state and local sales taxes, to enhance business-investment write-offs, to leave business meals fully deductible and to remove proposed limits on Individual Retirement Accounts (IRAs).

"Today was a very compatible day. We got rid of more small amendments than I expected," Packwood said last night. Asked whether he had the votes for final passage, he said: "I take it one vote at a time."

Among the measure's provisions for individuals:

*There would be two tax rates, 15 and 27 percent, rather than the current 15 rates, which range from 11 to 50 percent.

*The standard deduction would be increased to $3,000 for a single taxpayer, $4,400 for a single head of household and $5,000 for a married couple. Deductions such as those for IRAs (for taxpayers covered by other pension plans) and for interest on nonmortgage loans would be repealed.

*Other deductions, including those for mortgage interest on one or two homes, charitable contributions and all state and local taxes except for sales taxes, would remain. The deduction for charitable contributions for nonitemizers would expire, as is scheduled under existing law.

*The personal exemption for taxpayers and dependents, now $1,080, would be raised to $2,000 for most people, but not until 1988, a year after most other provisions would take effect. The personal exemption would be $1,900 in 1987.

The personal exemption for upper-income taxpayers would be phased out, hitting zero at $185,320 in taxable income on a joint return, $127,240 for a single taxpayer and $151,400 for a single head of household.

For single taxpayers, the 27 percent bracket would kick in for taxable income over $17,600; for married couples filing a joint return, the figure is $29,300. Income up to those figures would be taxed at 15 percent.

For the highest-income taxpayers, the 27 percent rate would apply to all income.

*Excise taxes on such products as gasoline and tobacco would not be increased, a change from earlier options discussed by the panel.

These changes and others would take 6 million lower-income Americans off the tax rolls, put 80 percent of all taxpayers in the 15 percent bracket, and reduce taxes for individuals by $100 billion over five years while raising corporate taxes by the same amount.

According to the Joint Committee on Taxation, the plan would cut the tax burden an average of 6.2 percent in 1988.

*A key provision affecting tax shelters would prohibit investors from claiming paper losses on investments in which they do not play a managerial role unless those investments generate income from which the losses can be deducted. One exception is real estate rentals, for which losses of up to $25,000 could be claimed against salary income for many taxpayers.

The provision would be phased in over two years.

Another cutback for upper-income taxpayers would end low effective tax rates on capital gains. Despite claims by some industries that raising these rates would harm innovation, the committee has given little consideration to watering down or phasing in the proposed change.

For businesses, the Packwood bill would reduce the tax rate from 46 to 33 percent. It would raise offsetting revenue by abolishing the investment tax credit, which subsidizes up to 10 percent of the cost of investment in new equipment, and by limiting the use of investment credits companies already hold.