through spending, lending and tax breaks -- far exceeds aid to the poor, according to a report released yesterday by Public Citizen, a group founded by Ralph Nader.

In a rare display of agreement with the Reagan administration, the report saluted President Reagan's fiscal 1986 budget proposal for attempting to cut more than half of the $24 billion in spending for private business.

It also noted that the Treasury Department's tax simplification plan would eliminate or modify many of the $83 billion in tax advantages for companies.

"Nader and Office of Management and Budget Director David A. Stockman have some things in common," said Jay Angoff, a staff attorney with Public Citizen and author of the study. "There are a number of people in the administration who are principled conservatives . . . but they get overruled by the Commerce Department types."

The report said the $107 billion in "corporate welfare" that it identified costs the U.S. Treasury more than Medicare, Medicaid, veterans' medical care and child nutrition programs combined.

The single largest piece of corporate largess identified by the report, which the group called "Aid for Dependent Corporations," was the investment tax credit, which gives firms a credit of up to 10 percent for investment. The group said the investment credit would cost the Treasury $38.4 billion in revenue in fiscal 1986.

Second on the list was the accelerated depreciation writeoff for the cost of new plants, equipment and real estate, which the group said would cost $21.7 billion in 1986. Other big tax breaks included tax-exempt industrial revenue bonds, at $4.5 billion; one-year writeoffs for research and development, $3.3 billion, and oil-industry drilling cost deductions, $2.7 billion.

If all these provisions were eliminated, however, it is unlikely that the federal deficit could be reduced by the same amount. Permitting business to write off its investment is standard tax policy, although there is disagreement about how it should be done.

On the spending side, the largest outlay was for the Commodity Credit Corp.'s array of farm programs at $12.6 billion. This is for all farmers, but the lion's share benefits the biggest farms, the study said.

Other items on the spending side included Rural Electrification Administration loans, $2.8 billion; the Export-Import Bank, which provides credit subsidies for exports, $996 million, and funding for inland waterways, $1 billion.

OMB spokesman Edwin L. Dale Jr. said he could not comment on the report because he had not seen it, but noted that most of the highest-cost items came from subsidies in the tax code.

Those proposals were not incorporated into the report's numbers, Angoff said. Instead, he used the "current services" categories of spending in the president's budget request, which estimate what spending levels would be if Congress took no action on the new proposals.