John A. Gronouski, a rumpled economics professor who parlayed an academic tax study and his ethnic background into a public service career that included stints as Postmaster General and Ambassador to Poland, died on Sunday in a hospital in Green Bay, Wisc. He was 76 and had lived in Green Bay since retiring in 1989 as a professor at the Lyndon B. Johnson School of Public Affairs at the University of Texas.

His family said the cause was complications from a stroke.

When he was tapped by President John F. Kennedy in the summer of 1963 to be Postmaster General, Mr. Gronouski was a highly regarded Wisconsin tax commissioner who had provided a crucial endorsement to Kennedy in the 1960 campaign.

Mr. Gronouski had a reputation as a militant Democrat from his role in an unsuccessful campaign to unseat Wisconsin's red-baiting Republican Senator, Joseph R. McCarthy, and as a tough-minded administrator who had revamped the Wisconsin tax system. But Mr. Gronouski had what many saw as an even more important political credential: his Polish background.

Mr. Gronouski was not only the first person of Polish extraction to serve in the Cabinet, he was also believed to be the first Cabinet officer to have actually earned a Ph.D.

Whatever reservations he may have had about being seen as an ethnic token in Presidential politics, Mr. Gronouski, whose mother was Irish, did not disappoint his patrons.

In his first 14 months in office, Mr. Gronouski, whose candor and pipe-smoking informality endeared him to the Washington press corps, held 63 news conferences, traveled 127,000 air miles, visited 132 cities and gave 445 speeches, an average of more than one a day, many of them to Polish-American groups.

But for all his political forays, Mr. Gronouski found time to become a highly effective postal administrator. Among other things he moved aggressively against racial discrimination in postal employment and spearheaded the transition to the five-digit ZIP code (after conceding that he did not know his own).

He also ordered bulk mailers to presort their own mail and moved to close many marginal post offices. It was a reflection of his unsentimental approach to postal economy that he endorsed a plan to save $4,417 a year by eliminating the rural carrier position in his own birthplace, the Wisconsin hamlet of Dunbar.

After being named Ambassador to Poland in 1965, Mr. Gronouski continued his barnstorming ways. Operating as what amounted to President Johnson's personal envoy to Eastern Europe, he used Poland as a base for what were billed as "bridge-building" trips to other Soviet bloc countries seeking to promote trade and other ties with the United States.

After President Johnson left office in 1969, Mr. Gronouski, who had helped run Hubert H. Humphrey's abortive bid for the Presidency in 1968, helped design the curriculum at the Johnson school in Austin and served as its first dean.

In 1977, he was called back to Federal service by President Jimmy Carter to become chairman of the Board for International Broadcasting, which ran Radio Free Europe and Radio Liberty.

Mr. Gronouski, who grew up in Oshkosh, graduated from the University of Wisconsin before serving as an Air Force navigator on bombing missions over Germany in World War II. When his plane was shot down, he was forced to bail out and survived even though he had worn his parachute upside down.

After the war, he earned his Ph.D. at the University of Wisconsin, held a series of teaching positions, including one at Wayne State University in Detroit and wrote a number of articles on tax policy, among them a study of the Wisconsin tax system that led to a job with the state tax department.

In 1960, less than a year after he passed a civil service exam to become research director, he was named tax commissioner.

He is survived by his wife, Mary; two daughters, Julie of Seattle and Stacey of Green Bay; a sister, Rita Wilson of Sun City, Ariz., and four grandchildren.

John A Gronouski