The Senate opens debate today on a dramatic overhaul of the federal income tax system, amid indications that senators of both parties may rebel against efforts by President Reagan and Republican leaders to whisk the bill through without changes.

Senators said they plan to fight for favorable treatment for Individual Retirement Accounts, capital gains, business meals and various investments, all of which would be curtailed or repealed by the package passed unanimously by the Senate Finance Committee last month.

"The 20 members of the Finance Committee had an opportunity to protect the special needs of their state," said Sen. Alan Cranston (D-Calif.), who said he would propose restoring deductions for IRAs. "Senators not on the Finance Committee didn't have that opportunity, and I think we should have it."

Nonetheless, the plan to slash tax rates to a maximum of 27 percent for individuals and eliminate many widely used deductions is expected to pass the Senate with few changes because of austere terms imposed on this year's debate by the effort to reduce the federal deficit.

Amendments to restore tax benefits must be coupled with offsetting tax increases so the bill would not increase the deficit. But opposition will arise to each tax increase, especially those threatening the dramatic rate cuts that are the heart of the bill's appeal, proponents said.

Votes are not expected on amendments until next week. With that schedule in mind, Reagan has invited all 100 senators to a White House breakfast Thursday to lobby against amendments.

Majority Leader Robert J. Dole (R-Kan.) and Senate Finance Committee Chairman Bob Packwood (R-Ore.) are working to keep the package intact. Packwood said 32 senators have promised to vote against all significant changes, although the Capitol was abuzz yesterday with talk of possible amendments.

Democratic senators emerged from a lunch session saying that many of them favor an amendment by Sen. George J. Mitchell (D-Maine) to create a higher tax rate of 35 percent for wealthy Americans and use the extra revenue to increase tax relief for low- and middle-income taxpayers.

Several senators objected to the speed with which the plan has come before the Senate. Those planning amendments said the overworked staff of the Joint Committee on Taxation had not given them revenue estimates necessary to formulate their proposals.

"A lot of us are deeply concerned about the pace this is going," Sen. Christopher J. Dodd (D-Conn.) said. "If you don't know the revenue implications of your own amendment, you're dead from the start."

Sen. John Melcher (D-Mont.) vowed to delay consideration of the package until he obtains data on whether farmers would suffer from the repeal of income averaging.

Packwood said he will file a petition today to limit debate on consideration of the bill, to prevent Melcher and others from delaying the bill indefinitely.

An amendment to continue more of the IRA deduction than allowed in the Finance package appears the most likely to prevail because of the tax break's widespread support among middle-income voters. Sens. Dodd, Cranston, Mitchell, William V. Roth Jr. (R-Del.), Alfonse M. D'Amato (R-N.Y.) and Max Baucus (D-Mont.) are among those planning IRA amendments.

Full restoration of the deduction would cost $26 billion in tax revenue over five years, an amount difficult to offset without removing other popular features of the bill.

"The bigger the amendment, the more political appeal it has, but the bigger problem and threat it is to the bill," said Sen. Bill Bradley (N.J.), one of few Democrats who have joined Packwood in opposing all amendments.

Even as some senators grew restive, others appeared to be bowing to Packwood's plea to hold their fire until a House-Senate conference committee reconciles the Senate package with a House bill passed last December.

Sen. Daniel Patrick Moynihan (D-N.Y.), who earlier advocated an amendment to restore deductions for state and local sales taxes, was weighing the possibility of proposing a non-binding resolution instead.

Democrats not likely to be on the conference committee were less sanguine, however. "The Senate would not be living up to its responsibility if we depend on conferees to rewrite the bill," Minority Leader Robert C. Byrd (D-W.Va.) said.

Even the chief Democratic conferee, former Finance Committee chairman Russell B. Long (D-La.) sympathized.

"If I were not a member of the Finance Committee and those boys hadn't taken care of Louisiana's interest and they tried to bind me to a no-amendments strategy, I'd laugh in their face," he said.