"To argue the benefits of moderation rarely brings honor or fame to an intellectual," says Neil Jumonville. Yet that is what Henry Steele Commager did, in a most immoderate era.

Unlike many of his liberal colleagues, the American historian did not enter the McCarthy period bearing a disillusioned leftist past. He had never been a leftist. He was a Jeffersonian, he said, and Jeffersonians didn't become Communists. He argued that whatever the dangers of domestic Communism, the extremes of anti-Communism posed a greater threat. As Mr. Jumonville shows in Henry Steele Commager: Midcentury Liberalism and the History of the Present (University of North Carolina Press; 328 pages; $49.95), Commager was a card-carrying pragmatist who believed in the value of dissent not just out of principle but on the grounds of society's practical need for a diversity of ideas.

The author shows how such views made him a target for the traditional right and for Sidney Hook and others of the Partisan Review school of Cold War liberalism, who thought him soft on Communism.

Mr. Jumonville uses his intellectual biography of Commager (1902-1998) to describe the ideological variety of liberals at midcentury and to consider how differences between cultural and political liberalism relate to the "culture wars" of today.

A problem in assessing Commager and his generation of liberals "is that they were swept aside by a flood of cultural change in the 1960s," writes the author, a professor of history at Florida State University. "This flow deposited midcentury liberals in a landscape very different from what they had inhabited, and it obscured their real political identities."

Mr. Jumonville also explores tensions in the lives of academics who combine scholarship with the activism of the public intellectual. Busy as a journalist and speech maker, Commager produced scholarly work that often exhibited "encyclopedic breadth at the expense of analytic depth," he writes. Although a riveting lecturer, Commager could be neglectful of his students. This escalated when he moved from Columbia University to the "monastic, tutorial, communal atmosphere" of Amherst College. At Amherst, Commager didn't always bother to learn his students' names, often calling them by the names of the authors they were writing papers about. Friends chided him for flightiness. "Quicksilver Commager, I call you," wrote his fellow historian Allan Nevins, "brilliant, attractive, gleaming, and when the finger closes down on you, somewhere else!"