Ralph Nader, who crusaded against defects in the Corvair, duplicity in the Congress and dishonesty in Corporate America, has taken aim on a new target.

It is the Reaganites, portrayed by Nader as wealthy presidential friends "remote from the realities of life for most Americans" who look out for the welfare of big corporations but treat the poor with "mindless neglect."

"This is, unabashedly, a government of the wealthy," Nader concludes in his introduction to "Reagan's Ruling Class," a 750-page book written by Nader activists Ronald Brownstein and Nina Easton that attempts to profile the top 100 officials of the administration.

The Reagan "regime," Nader writes, "is foremost a homogenized government by elites. Even organized labor leaders are out; also gone are the minorities, the poor, the elderly, consumers and environmentalists."

At a press conference yesterday to promote the book's release, Nader described the administration as a government "of General Motors, by DuPont and for Exxon," run by people "who view the federal government as an instrument for the powerful and the wealthy, unaccountable to the public."

The result of a year's research into the background, convictions and decisions of the top 100 Reaganites, the book, which was published by Nader's Presidential Accountability Group and will sell for $24.50, follows a similar effort to profile members of Congress several years ago.

Brownstein, 24, and Easton, 23, said they conducted more than 500 interviews over 12 months for the new book.

Like the congressional study, which created controversy and was criticized for inaccuracies, Nader's latest effort is certain to draw fire as a one-sided view of an administration Nader finds the antithesis of his own pro-consumer, anti-corporate convictions.

Nader, the nation's best-known consumer activist, saw many of his proteges enter government during the Carter years and now believes their work is being undone in the Reagan era.

In their research, the Naderites found that, like President Reagan himself, many of the people brought into his administration have made an ideological journey to conservatism. They also found in the speeches and newspaper reports of the past activities of many Reagan appointees comments they would be unlikely to make today.

For example, Defense Secretary Caspar W. Weinberger, once a liberal San Francisco Republican, told a seminar at the American Enterprise Institute in 1972: "The identification of a threat to security does not automatically require an expenditure in the defense budget to neutralize it. . . . The defense budget, in short, must be seen not only in terms of what we must defend ourselves against, but what we have to defend. The more we take from the common wealth for its defense, the smaller it becomes."

Of the 100 administration officials profiled by Brownstein and Easton, they said 98 were white, 95 were men and more than 30 percent were millionaires. Of the 100 officials, 57 consented to interviews, some conducted with Nader. Some sessions produced revealing moments, such as when CIA Director William J. Casey was asked about his greatest triumph, and replied: "If I get out alive . . . , after you've been shot down . . . , I'd say the thrill is to be still here."

But the volume suffers from a lack of access to top White House officials, none of whom agreed to interviews for the book. Nader, in his comments yesterday and in his introduction to the book, put great stress on the so-called "Kitchen Cabinet" of Reagan's friends.

Nader said Reagan's appointments were "directed" by this group of "evangelists of a corporatist political ideology," in the "hard core" of which he includes Attorney General William French Smith, formerly a Los Angeles corporate lawyer; industrialist Justin Dart; southern California auto dealer Holmes Tuttle; real estate developer William A. Wilson; oilman Henry Salvatori; steel magnate Earle Jorgensen, and beer mogul Joseph Coors.

While these men have all played a role in Reagan's political career or campaigns at one time or another, they were not all instrumental in Reagan's appointment decisions. Smith, for example, was influential in the process, but Dart clearly was not.

Searching for the human side of the Reagan administration that Nader said he hoped would make faceless officials into "household names like athletes and actors," the authors present some personal glimpses.

In 1973, they report, Interior Secretary James G. Watt, then director of the department's Bureau of Outdoor Recreation, was trying to ease out a subordinate, Roy Wood. After telling Wood he wanted him to leave the government, Watt said, "let us pray about it" and "down on our knees we went," Nader quotes Wood as recalling.

Wood's wife, Matilda, also is quoted as saying Watt called her later and said, "He had talked with the Lord and the Lord felt that we should return to Georgia their home state ."

A spokesman for Watt said yesterday there was "no truth" to the story.

The authors also report that when Weinberger went to brief Reagan on what he argued would be the adverse impact of Office of Management and Budget Director David A. Stockman's budget cuts, the defense secretary took with him 32 cartoons. Rather than the usual charts and graphs, the visual aids were designed so as not to "drown" Reagan in detail, the book claims. "One chart used three different mushroom clouds to indicate the difference between the military budget Carter left behind, Weinberger's proposed defense levels, and the effect of Stockman's cut . . . ."

Yesterday, Nader said he was struck by the universal "lack of compassion" among Reagan's top officials. The "most coldblooded," he said, is Transportation Secretary Drew Lewis, for being "grossly indifferent" to highway safety issues. The "brightest" in the Reagan Cabinet is Treasury Secretary Donald T. Regan, Nader said, while he described Energy Secretary James B. Edwards as the "least competent and least informed."

The most liberal? "Look as we could, we couldn't find a liberal," Nader said. CAPTION: Picture, Nader at release of 750-page profile of Reagan administration. It sells for $24.50. AP