Conservative professors must publish more than their liberal peers to be competitive for the same university jobs and promotions, according to new reports. At a conference sponsored by the American Enterprise Institute today in Washington, D.C., researchers from across the country will present 18 papers that they say document the growing liberal bias in academia.

“Universities are tilting to the left, and it starts at the student level and goes all the way through to the hiring level and even to the promotion level,” the vice president and director of the National Research Initiative at AEI, Henry Olsen, said. “This is a real problem, not anecdote masquerading as fact.”

In departments such as sociology and anthropology, “progressive” and “liberal” professors outnumber “conservative” and “libertarian” faculty members by a margin of at least 20 to 1, according to a new study by a husband and wife research team from George Mason University and the Swedish Institute for Social Research. The findings are based on dozens of national surveys about faculty voter behavior, policy views, and voter registration.

Some professors said a liberal bias is damaging the intellectual vitality of campus life, and they discourage conservative students from pursuing doctorate degrees in the humanities.

“If my students show conservative bias, I steer them away from the academy,” a professor of English at the University of Virginia, Paul Cantor, said. “They have no future — they will not get jobs. If they want to teach traditional works in a traditional matter, they have no future in an English department today.”

Mr. Cantor, who is spending a semester at Harvard University teaching a course on Shakespeare and politics, said English departments were more intellectually diverse 50 years ago than they are today. Professors today may have broadened their syllabi, but most of them interpret those texts through the uniform lenses of race, class, and gender, he said.

“English departments have been homogenized in the name of diversity,” Mr. Cantor said. “Precisely for the reason that liberals feel underrepresented and marginalized in the country, they relish the position in the academy where they’re in the overwhelming majority.”

Using national surveys that measured political party registration and ideological self-designation of faculty at 183 randomly selected four-year colleges and universities, researchers concluded that ideology had about a third as much impact as merit in determining the career success of socially conservative university professors.

The trend is worrisome to many conservative scholars. “It hurts academia,” a professor of Political Science at Villanova University, Robert Maranto, said. “It limits the questions we academics ask and the phenomenon we study, limiting the ideas which undergraduates are exposed to during their college education.”

Some critics of the studies said it was misleading to assume that a professor’s political ideology would translate into bias in the classroom or the departmental meeting, where tenure decisions are made.

A professor of economics at George Mason University, Daniel Klein, said majority politics ultimately affects hiring decisions by the department.

“It has become commonplace for boards and presidents to exercise little or no oversight of academic hiring,” the president of the American Council of Trustees and Alumni, Anne Neal, said. “If we are to reform the politically correct university, alumni and trustees must take notice and take action.”

The reports will be published next year by AEI in a book titled “Reforming the Politically Correct University.”