The consummate tough-guy persona of Humphrey Bogart. The vulnerability of James Stewart. The bad-boy sexuality of Marlon Brando. The romanticism of Cary Grant. It would not be hard for a moviegoer to end up wondering whether masculinity is a mode of performance.

This, as it turns out, is the conviction of a growing number of scholars in the field of so-called masculinity studies, a somewhat surprising offshoot of feminism in which mostly male academics have taken feminist theory and applied it to the study of masculinity and men.

Masculinity studies are not part of any antifeminist backlash. Practitioners do not talk about male bonding or affirming traditional male values. Instead, they have been inspired by a central principle of feminist theory, that gender is not inborn but created, that gender is performance.

Over the past few years, scholars in fields like sociology, history and film studies have tried to dissect how manhood has been ''constructed,'' as they put it, examining everything from its shifting representation in movies to what men's letters and diaries reveal about their roles over time.

Their conclusion is that masculinity is not monolithic. The masculine ideal varies widely among groups and often varies by age, region and race, they say. It changes as circumstances change over time, often in response to historical and cultural change.

''What male scholars started doing was they said, 'What if there is more than one masculinity?' '' said Dennis Bingham, an associate professor of English at Indiana University-Purdue University and the author of a book on masculinity in the movies of James Stewart, Jack Nicholson and Clint Eastwood. '' 'What if masculinity is a construction, something we unconsciously work very hard on making ourselves into that we've all conned ourselves into believing is natural?' ''

In ''American Manhood: Transformations in Masculinity From the Revolution to the Modern Era'' (Basic Books, 1993), E. Anthony Rotundo, a historian who teaches at Phillips Academy in Andover, Mass., divides manhood over the past 250 years into three distinct phases.

In Colonial New England, the dominant form was ''communal manhood,'' he writes. A man's identity was defined by his usefulness to his community. With the rise of a market economy and the growth of the middle class, that form was eclipsed in the early 19th century.

''Self-made manhood'' supplanted it, Mr. Rotundo says. A man's identity and social status came from his achievements more than any accident of birth. Ambition, rivalry and aggression were given freer rein, he writes; manhood depended on channeling, rather than moderating, his passions.

By the late 19th century, there was another shift: combativeness had become a positive male virtue, the book argues. Competitiveness was exalted, toughness admired, tenderness scorned. Male sexual desire, seen earlier as worrisome, became an important part of the new ''passionate manhood.''

Images of masculinity appear to shift even more on screen than in real life. Steven Cohan, an English professor at Syracuse University, devotes his book ''Masked Men: Masculinity and the Movies in the 50's'' (Indiana University Press, 1997) to tracking the contradictory images of manhood in postwar films.

Masculinity was in flux, Mr. Cohan writes. The war had shaken up gender relations at work and at home, and anxiety about the mental stability of returning veterans had ''exaggerated the danger their ungovernable masculinity posed to the social order.''

The politics of the cold war, too, projected contradictory messages for manhood, Mr. Cohan writes. A ''hard'' masculinity was required for defending the nation's borders, but a ''soft'' masculinity was insisted upon as ''the foundation of an orderly, responsible home life.''

That complex mix of historical and cultural pressures influenced what Mr. Cohan calls ''the masculine masquerade'' he finds in movies of the 1950's, which he examines in the on- and off-screen images of actors like Grant, Bogart, Brando and William Holden.

''Though men have supposedly been invisible, looking at how their bodies appear in film can reveal the same kind of shifts that looking at the female body in film does,'' Mr. Cohan said recently, giving as an example the contrast between the exoticism of Rudolph Valentino and the athleticism of Douglas Fairbanks.

The roots of masculinity studies as a field can be traced to the mid-1970's, when a group of men, mostly social psychologists, began using feminism to examine their own lives. Out of that effort came the first two anthologies of scholarly articles on masculinity and a national conference on the subject.

By the late 1980's, a couple of professors in sociology and history departments were teaching courses on manhood and masculinity, relying on stacks of photocopies for the reading. Since that time, there has been a steady stream of books and articles on the subject, including ''Manhood in America: A Cultural History'' (The Free Press, 1995) by Michael Kimmel, a professor of sociology at the State University of New York at Stony Brook who teaches a course on masculinity and edits a quarterly journal for the field.