A major new book sharply critical of Army leadership in Vietnam and supposedly written by a "senior field-grade officer . . . currently assigned to the Pentagon" using the pen-name "Cincinnatus" was actually written by a professor who was never in Vietnam and whose affiliation with the military since 1965 has been as a chaplain in the National Guard.

In a lengthy telephone interview yesterday, Dr. Cecil B. Currey, 48, a history professor at the University of South Florida in Tampa, acknowledged that he is "Cincinnatus," author of Self-Destruction: The Disintegration and Decay of the United States Army during the Vietnam Era, published by W. W. Norton & Co. in New York early this year.

The book has received wide-spread national attention. It has been reviewed by major newspapers around this country and abroad. Numerous anonymous telephone interviews were arranged by the publisher in which reporters did not know the identity of the author. "Cincinnatus" also appeared on the NBC-TV "Today" show with his face hidden by shadow and his voice electronically disguised.

Despite this author's anonymity, the book has received widespread acclaim in most reviews.

But in many cases the reviewers or interviewers apparently assumed too much about the author's credentials or possibly were misled by the way the publisher described "Cincinnatus" on the book jacket or by other factors, including previous interviews.

"Today" show reporter Jessica Savitch, for example, introduced him on Feb. 2 as a "career military man . . . a Vietnam veteran . . . right now assigned to the Pentagon." There was no attempt by "Cincinnatus" to refine that description on the air.

Herbert Mitgang, a New York Times reporter who covers publishing, wrote Dec. 30 about the book's impending appearance. He had a telephone interview with "Cincinnatus."

The author, Mitgang reported, said he had served as a private and corporal in Korea, was commissioned in 1962, graduated from the Command and General Staff School and Army War College, and served as a captain during the 1968 Tet offensive.

His editor at Norton, Eric P. Swenson, told Mitgang at the time that he had checked the colonel's credentials, had spoken to him many times but had never seen him in person.

The book jacket describes "Cincinnatus" as "the pen name of a military man who entered service as a private in Korea and rose through the ranks to become a senior field-grade officer. A graudate of Command and General Staff College, he is the author of one book on military history as well as papers and monographs. He holds A.B., M.A. and Ph.D. degrees. He is currently assigned to the Pentagon."

According to Army records and yesterday's interview with Currey, the professor joined the Army as a private June 30, 1953, just days before the Korean War cease-fire. He did not serve in Korea. He left the Army in 1955, staying in the inactive reserves, then completed a master's degree and entered the ministry.

He left the ministry in 1962, got a doctorate in history at the University of Kansas, then joined the Nebraska National Guard in 1965 and applied for a commission as a first lieutenant in the chaplain corps in an effort to retain links to his twin interests: the ministry and the military.

Currey transferred to the Florida National Guard, where he stayed from 1967 to 1978, doing weekend and two-week-a-year stints of active duty as a chaplain while teaching at the University of South Florida.

In 1975, he spent a term as a resident student for the Army's Command and General Staff College, which he says was a unusual compliment for a reserve officer, and eventually became a faculty consultant. In 1978, as a major, he transferred from the guard to become a lieutenant colonel in the Army reserves to qualify for a reserve post in the Chief of Chaplains Office in the Pentagon.

Currey, who still lives in Florida and teaches at the university, acknowledges that his duties in the Pentagon are like those of reserve or guardsmen elsewhere, namely two weeks a year of active duty, though he has taken on some special projects which have kept him at the Pentagon a few weeks longer on occasion.

In the event of a full reserve mobilization, he would be assigned to the Pentagon. This may account for the "currently assigned to the Pentagon" line in the book jacket.

Currey did not go to the Army War College, and while he was a captain during the Tet offensive in Vietnam in 1968, he was in Florida at the time.

Currey says those items in The New York Times interview caused him great personal grief, and he said he thinks they were basically a misunderstanding because he and the reporter were talking about Tet and the reporter asked what his rank was at the time. Currey claims he has tried to be as carefully as possible in interviews.

Currey's book received considerable praise in the lead review in The Washington Post's Feb. 15 "Book World." The review was written by Josiah Bunting III, a former Army officer in Vietnam, college president and author of The Lionheads.

In that same edition, a separate interview with "Cincinnatus" by reporter Marc Leepson and arranged by the publisher referred to the anonymous officer as an Army colonel stationed at the Pentagon who had served a tour of duty in Vietnam.

The book is an April selection of "The Military Book Club," and the brochure that went out to thousands of members carried the headline: "Why We Lost in Vietnam" and talked about "a scathing critique of the U.S. military by an officer who was there."

It said the book was "written by a career officer who served in Vietnam and is now assigned to the Pentagon" and is based on "his own 30 years of military experience."

Currey said he and Swenson were very upset by this and wrote a letter to book club officials asking where they got their facts and referring them to the book jacket as the only authorized description. Nowhere in the book, Currey said yesterday, is the claim made that the author was in Vietnam.

The central theme of Currey's book is very blunt: "The old, old refrain that the Army failed because of political and social unrest at home is still the theme song of the uppers ranks. The fact is that the military disaster in Vietnam grew out of ineptitude at the top.

"Stated simply," Currey wrote, "the Army made too many mistakes in its years in Vietnam. If those same errors are not to be repeated in some future conflict, their sources must be identified, understood and corrected. At some point, for reasons then believed good, America's Army will once again be sent into battle. It will be unfortunate if it has closed its eyes to the lessons of Vietnam and again faces a debacle."

The reviewer for The Philadelphia Inquirer, echoing a feeling that was evident in a number of media reviews, said: "This book should be urgently and widely studied in Washington with immediate steps taken to eliminate the weaknesses it reveals. The author deserves a medal for what he has written."

Military reviewers were far more skeptical. While admitting that there were many lessons to be learned, they challenged the book's tone, scholarship, authenticity and the idea that the Army, rather than the political leaders, deserved all of the blame.

Col. Harry G. Summers Jr., an infantry colonel on the staff of the Army War College, wrote in "Army" magazine that it was the ultimate in "chutzpah" for "a self-proclaimed Army officer who supposedly rose from the ranks" to condemn officers for not resigning over their disagreement on Vietnam policy and then publish his attack on the Army anonymously.

In his book, "Cincinnatus" wrote, "In certain churches, ministers wear dark clerical garb to obscure as much as possible of themselves in order to allow their listeners to concentrate exclusively upon what is being said rather than upon who is saying it. That is my hope here as well."

In the interview, Currey said the dilemma he and his editor faced was how to get an important message across to an institution, meaning the Army, that is by its nature suspicious of criticism whether it comes from within or without.

If he were identified as a civilian, he said, the question would be asked what he knows about the Army. If his military credentials were used, he would be dismissed also because critics would focus on his rank, his lack of Vietnam service and, most of all, on being a chaplain.

"No matter how we presented the biography," Currey explained, it was felt that the authority of the credentials "would stand in the way of getting a serious hearing for an important message." So a pseudonym was used in the hopes that readers would not get hung up on who wrote it, he said.

Cincinnatus, according to legend, was the 5th Century Roman citizen-soldier-patriot who left his farm, was made dictator long enough to save Rome, and then renounced his title and returned to the farm.

Currey says he, in person or as the fictional "Cincinnatus," is also "dedicated to this Army" of today.

Initial information concerning the identity of "Cincinnatus" came from Army officers who had received anonymous letters alleging that Currey was the author. This information was passed on to The Washington Post.

Additional inquiries in many other places, including the University of South Florida, made it clear that Currey was the author. Attempts to reach Currey for several days were unsuccessful, but were finally arranged by the publishers.