President Reagan appears to be losing support for his tax reform campaign from the leaders of big business, who see the risks of reform moving steadily ahead of the likely benefits.

"I think most of us started out very strong on tax reform," said Stephen D. Bechtel Jr., chairman of Bechtel Group Inc. But that support is eroding because of a growing fear that a restructuring of the tax system will leave business significantly worse off than it is now, he said.

"The package will not be as good as what we've got now. I think you'd find that's the sentiment of most of the people here," said Bechtel, one of the chief executives of major companies attending the fall meeting of The Business Council at The Homestead. He added that, "I think that's said with great regret."

The fear expressed by a number of the Business Council members is that the additional reduction in individual taxes promised by Reagan in the form of an increased personal tax exemption will be paid for, in large part, by business. Second, they fear that the payment by business will come in reduced tax benefits for capital investment.

There is now a recognition among business leaders that they will have to give something substantial in order to retain investment tax incentives, said Rep. James R. Jones (D-Okla.), who spoke to the Business Council members on Friday. That something substantial is a minimum corporate tax, assuring that no major company could completely escape federal tax payments.

"They recognize the issue of fairness is not going to go away," Jones said. Striking such a bargain will not be easy, he said.

There was no formal poll of Business Council members available to document a decline in support for tax reform, and some business leaders said their enthusiasm remains strong. But interviews with nearly a dozen of the Council members backed up Bechtel's view.

"Nine out of ten would be against it," said John F. Akers, president of IBM Corp. "I'm not one of them.. . . IBM is still on the tax reform bandwagon. I hope I don't fall off."

"I didn't see much support for major tax reform in this group," said Jones, a key member of the House Ways and Means Committee. "There is none," said James D. Robinson III, chairman of American Express Co.

"The budget deficit simply overwhelms any element of tax reform," said George M. Keller, chairman of Chevron Corp. "I'm concerned that we've got all this effort concentrated on something that's really premature, and it's almost a panicky effort to get something out in a matter of weeks."

Another guest at the Business Council meeting was Deputy Secretary of Treasury Richard G. Darman, who insisted it was still too early in the development of tax reform legislation to be tallying votes from the business community.

"Many businessmen are enthusiastic about tax reform and many are not," Darman said. "Most are in the stage of prudent observation." Darman predicted that the final tax reform bill won't resemble either of the Reagan administration's two reform proposals or a version introduced recently by House Ways and Means Committee Chairman Dan Rostenkowski (D-Ill.) "The time to judge is not now," Darman said.

Roger Smith, chairman of General Motors Corp. also urged a wait-and-see position. "I'm betting on tax reform but I can't cash my ticket yet because he Rostenkowski is still half way around the track. We haven't had a real shot at tax reform in this country for a long time. . . . We shouldn't give up yet."

But there appeared to be an increased anxiety among Business Council members that the tax reform process will inevitably cut into the substantial incentives for capital investment that business received in the 1981 tax bill. That conclusion was offered to Council members by Martin Feldstein, former chairman of the Council of Economic Advisers in the first Reagan term and now president of the National Bureau of Economic Research.

Feldstein said that both the administration's tax bill and Rostenkowski's would damage the process of capital formation, and thus harm productivity and economic growth in two ways: They would reduce the chances of dealing with the budget deficit; and substantially increase the cost of funds and effective tax rates on investments in plant and equipment.

"While I was an advocate of tax reform, and I am an advocate of tax reform, I think the direction that tax reform is currently going is just wrong, and what we have to do is either move toward a very substantial redirection, which I doubt the Senate would be willing to achieve, or forget about it this time around and come back to it later when we can have a tax reform that will strengthen economic incentives" for business investment, Feldstein said.

Privately, some Business Council members express frustration over their inability to sell their position on tax reform, budget deficits and trade to the White House -- particularly now that one of their one-time colleagues, former Merrill Lynch chairman Donald Regan, is the president's chief of staff.

"It's clear they're not listening," said Edmund T. Pratt Jr., chairman of Pfizer Inc.

Allen Sinai, chief economist of the brokerage firm Shearson Lehman, said the incentives for investment provided in 1981 amounted to a kind of social contract with business. "The administration almost has broken faith four years later by supporting and presenting a plan that removes the investment tax credit and diminishes accelerated depreciation," he said.

"It took us 10 years to finally get ACRS," said Reginald Jones, former chairman of General Electric Co., referring to the Accelerated Cost Recovery System enacted in the 1981 tax bill that substantially increased tax deductions for business investment. "And now you're going to take that economic weapon away." The manufacturing sector, in particular, needs those tax benefits now more than ever because of the pressure of foreign competition, he said.

Robert A. Beck, chairman of Prudential Insurance Co. of America, said another problem with the tax reform debate is the uncertainty it is causing among investors. "There are whole chunks of our business that are not moving while people wait to find out what the law is going to be . . . .The tax shelter business has been very badly damaged by just having to wait and not being sure what is going to happen."

Despite the growing concerns about tax reform, however, there appears to be a consensus among the Business Council members that some kind of tax reform bill will pass next year. Robinson of American Express is one of those members who believes there will be some kind of tax bill by next year. "The target now is to get into (House-Senate) conference," he said. Once the legislation reaches the conference committee the real negotiations over tax reform will begin.