The Senate Finance Committee, which resumes work on rewriting the tax code today, is close to a compromise on widely used investment write-offs for business.

If members of the committee and the Reagan administration can agree on how to soften proposals on depreciation by Finance Committee Chairman Bob Packwood (R-Ore.), they will have overcome one of the biggest obstacles to producing a tax revision bill.

But as the committee picks up after the Easter congressional recess, Packwood also will face increasing pressure from oil-state senators to take action to offset the harm to the industry from declining oil prices. And yesterday he agreed to hold hearings on his controversial proposal to end the deduction companies take for the excise taxes and tariffs they pay, thus increasing the opportunities opponents of that provision will have to air their views.

The Finance Committee is scheduled to consider this week the portions of Packwood's tax proposal dealing with trusts and estates, pensions and taxation of companies operating abroad. Committee aides said senators are expected to have amendments to propose in all those areas. Packwood plans to work on tax overhaul practically nonstop until the end of the month.

Depreciation -- as investment write-offs are known -- has been skimmed over once by the committee. But it could come up for amendments if Finance members, Packwood and Treasury Department officials agree on a compromise. His plan would repeal the investment tax credit, which pays for up to 10 percent of the cost of investment in equipment and machinery, and would lengthen the periods of years over which investment costs for real estate, equipment and vehicles can be deducted.

The compromise would increase the deduction that can be taken in the early years of those periods, "front-loading" the benefit to make up for loss of the investment credit. It would only apply, however, to a new class of "productive" equipment that would include equipment used in manufacturing, oil and gas, transportation, communications, research and, possibly, oil refineries.

The possible compromise also would be more generous to write-offs for cars and light trucks used in business. The Packwood plan to deduct those expenses over five years instead of the current three years drew heavy criticism from committee members. And the compromise is likely to call for linking depreciation write-offs fully to inflation, expanding on the partial inflation-indexing proposal made by Packwood.

Amendments also are expected in the energy area, which the committee sped through during its first day of tax-writing two weeks ago but to which Packwood has promised to return. Such Finance members as Sen. David L. Boren (D-Okla.) are looking at ways to help the oil and gas industry recover from oil prices that fell briefly below $10 a barrel last week.

On Sunday, Treasury Secretary James A. Baker III endorsed repeal of the windfall profits tax on oil, an idea that could well be offered in committee and which has the advantage of costing little federal revenue. Because of the way the tax is related to oil prices, it is bringing in very little money at the moment.

For the same reason, however, repealing it would do little to help the industry, and Boren also is looking at a tax credit for production from low-volume wells and expansion of the oil depletion allowance, among other options.

Packwood's position on those proposals is not known, but several congressional sources pointed out that new tax deductions and credits can do little to help sick oil firms, which can't use tax breaks if they have no taxable income.

The depreciation plan and any additional energy benefits all would reduce the tax revenue that the proposal would collect -- the depreciation compromise alone could cost $20 billion over five years -- making it necessary to increase taxes in other areas to avoid increasing the federal deficit.

Like the legislation passed by the House late last year, the Packwood plan would reduce individual and corporate tax rates while curtailing numerous deductions and credits. Both measures would shift more than $100 billion in taxes from businesses to individuals over five years.

But Packwood's plan includes an additional wrinkle: Repealing the excise tax and tariff deduction and raising existing excise taxes on alcohol, tobacco and gasoline would raise about $75 billion over five years. That proposal has encountered opposition on the committee from such Democratic senators as George Mitchell (Maine) and Bill Bradley (N.J.), as well as from affected industries and consumer groups fearful it would lead to higher prices.

Hearings on that element of the Packwood plan would in all probability put the spotlight on that opposition. A date has not been scheduled, but they are expected to occur this month or in early May.