In a series of letters in recent years, William D. Ruckelshaus has taken issue with figures as diverse as Gerald R. Ford, Laurance S. Rockefeller and the president of the Audubon Society in defense of his belief that the social benefits of environmental rules must be balanced against their economic costs.

The letters were made available to the Senate Environment and Public Works Committee by Ruckelshaus and the Weyerhaeuser Co., where he has been senior vice president since 1975. The committee is scheduled to hold hearings next week on Ruckelshaus' nomination to head the Environmental Protection Agency.

In a 1976 letter to a high-level Labor Department official, Ruckelshaus lamented that President Ford was probably too pro-business to be able to pull off regulatory reform.

"Because of the president's inhibitions against drawing any daylight between himself and big business, I find it very difficult to believe that he is going to be successful in effecting regulatory reform," Ruckelshaus wrote. "Just as it took Nixon to open up the window to China, it may take Carter to bring light and progress to the regulatory reform effort."

The letter was written to Henry H. Perritt Jr., then in charge of economic policy review at Labor. It and others collected by the environment committee provide an unusual and candid portrait of Ruckelshaus as a man of the middle, bothered by both extremes in the environmental debate.

Among the letters, for example, are:

* A 1980 missive to an Audubon Society official, accusing Audubon President Russell Peterson of attempting to "curry favor" with local environmentalists by criticizing a business facility owned by Weyerhaeuser. "I had hoped that some of us could rise above the knee-jerk anti-business sentiment so often found in the environmental movement," Ruckelshaus wrote. A notation indicates that a copy was sent to Peterson.

* A letter the same year to wealthy industrialist Laurance S. Rockefeller, brother of the late Nelson A. Rockefeller, declining to endorse Rockefeller's effort to publicize the need to protect sensitive coastal areas. "My impression of the materials you have sent me is that you intend to emphasize preservation over development," Ruckelshaus wrote. " . . . In my opinion any program which does not seek to preserve with rational development will so embroil us in additional controversy that neither rational development nor preservation will result."

* A 1979 letter to the president of the American Farm Bureau Federation, in which Ruckelshaus refuses, on behalf of Weyerhaeuser, to support a conference on the use of the pesticide 2,4,5-T. The federation, like Weyerhaeuser, supports expanded use of the controversial pesticide, but Ruckelshaus warned that background documents for the conference lacked objectivity and appeared likely to "fuel the emotionalism of the debate."

The letters were delivered to the Environment Committee by Weyerhaeuser, which had been asked to supply all the company's policy statements on matters handled by the EPA, as well as letters written by Ruckelshaus on environmental matters while he was employed by the firm. The committee released the documents Thursday, after formally receiving Ruckelshaus' nomination.

Included in the thick packet are more than two dozen letters signed by Ruckelshaus, ranging from a one-page note to a retired Navy vice admiral seeking information about a deer repellent to a five-page outline of strategy to ease the Clean Air Act, addressed to Vice President Bush.

The central theme of many of the letters is "regulatory reform," a term Ruckelshaus applies to efforts to weigh the expected cost of a government rule against its potential benefits.

As Ruckelshaus predicted in his 1976 letter to Perritt, the Carter administration used the idea to initiate cost-benefit analyses of dozens of proposed rules. But the phrase has become a political red flag for environmentalists and consumer groups, who say the concept is being used to spare industry millions of dollars in cleanup costs at the expense of the public health.

The controversy has been intense at the EPA, where it fueled allegations of a pro-industry and political bias that eventually led to the resignation March 9 of former administrator Anne M. Burford.

But, in his letter to the American Farm Bureau Federation official on the 2,4,5-T conference, Ruckelshaus attempts to draws a distinction between "Political" decisions that result from outside pressure and "political" decisions that result from regulatory efforts that balance benefits and costs.

"If you detect a note of outrage in my letter, you are correct," Ruckelshaus wrote, complaining that the federation had misstated his reason for banning the pesticide DDT in 1972. The background paper apparently referred to the decision as a "political" one.

"Political . . . is used in a pejorative sense as being the result of unwarranted pressure," Ruckelshaus wrote. "Politics with a capital 'P' had nothing to do with it . . . .

"Decisions by the government involving the use of toxic substances are political with a small 'p,' " he wrote. "Political in the sense that it reflects a society weighing what risks it is willing to accept in return for what benefits."

The letters have been scrutinized carefully by senators preparing for three days of hearings on the Ruckelshaus nomination next week. Of particular interest to many members is Ruckelshaus' position on the Clean Air Act, which has strong backing on the Environment Committee.

An aide to Sen. George J. Mitchell (D-Maine), who helped write amendments to the act, said Mitchell was particularly concerned about Ruckelshaus' statement in a 1981 letter to Bush that it is "irrational" to base national policy solely on health or environmental effects.

"Mitchell feels on the contrary that it's entirely rational and appropriate, and that Ruckelshaus is dead wrong," said the aide.