If you were a high-ranking Reagan administration official, would you sit down and chat about your life and politics with Ralph Nader?

A year ago, Nader and two colleagues, Ronald Brownstein and Nina Easton, began research for a book due out next month featuring profiles of Reagan's senior staff, regulatory agency heads, cabinet and subcabinet officers.

"In an administration high on symbolism, rhetoric and slogans, there needed to be a sharper focus on the kind of people who run the executive branch," says Nader, who decided a book titled Reagan's Ruling Class: Portraits of the President's Top 100 Officials might just fill the bill. He didn't expect much cooperation from his subjects, but to the veteran crusader's surprise, 57 of the president's 100 senior men and women agreed to cooperate with the project that marks Nader & Co's first such examination of the executive branch.

"It's pretty straight," says Nader of the 650-page hardback book that will sell for $21.50. "There are no ratings."

But Nader is willing to rate some of the Reagan officials according to how they handled themselves during the compilation of the book. Most Accessible Departments

Department of Defense ("I was surprised," says Nader. "Seven out of eight people talked with us." That included Secretary of the Navy John Lehman who, asked about the jellybeans on his desk, joked, "Well, there's quite a sweet tooth in this administration for the military.")

U.S. Arms Control and Disarmament Agency (Three out of three, including director Eugene Rostow, granted interviews)

Department of Justice (Five out of seven) Least Accessible Departments

Department of State (One out of eight)

White House (One out of five)

Department of Energy (One out of seven) Most Relaxed Interviewees

Secretary of the Air Force Verne Orr

Deputy Secretary of Defense Frank Carlucci

Secretary of the Treasury Donald Regan Most Candid

Associate Attorney General Rudolph Giuliani

Government Printing Office chief Danford Sawyer ("He told us his congressional oversight committee should quit," says Nader.)

Council of Economic Advisers member William Niskanen Jr. Most Uptight

Environmental Protection Agency administrator Anne Gorsuch

Federal Trade Commission chairman James Miller III

Secretary of Transportation Drew Lewis Heaviest Smokers

Bureau of Land Management director Robert Burford

EPA administrator Anne Gorsuch ("While we were talking about carcinogens," recalls Brownstein)

Assistant Attorney General William Baxter (Antitrust Division) Most Verbose

National Highway Traffic Safety Administration Administrator Raymond A. Peck Jr.

Raymond Peck Jr. Most Resistant To Interviews

Attorney General William French Smith "He agreed to answer written questions," says Nader, "but we got no reply.")

White House deputy chief of staff Michael Deaver ("He even refused to supply a picture until the last moment.")

Secretary of Labor Ray Donovan

Secretary of Health and Human Services Richard Schweiker

Office of Management and Budget director David Stockman

In the course of trying to secure interviews, Nader and his assistants encountered the most hostility from ACTION director Thomas Pauken, who, Nader says, told him he "knew" what he was going to write, so there was no profit in his cooperation. Securities and Exchange Commission chairman John Shad and Assistant Attorney General William Reynolds of the Civil Rights Division also, says Nader, were wary of talking and, in the end, declined interviews.