President Reagan has chosen Edward A. Curran, deputy director of the Peace Corps and former National Cathedral School headmaster, to be the next chairman of the National Endowment for the Humanities, according to administration and endowment sources. But the nomination is being stalled by administration moderates lobbying for a less controversial and conservative alternative, they say.

Publicly, administration officials blame routine security checks for the delay in forwarding the nomination to the Senate.

Privately, however, they and congressional sources say that a campaign is under way to give the nomination to one of a half-dozen or more scholars whose names have circulated since William J. Bennett left the post earlier this year to become secretary of education.

Leaders of the museum, university and scholarly groups that represent many of the recipients of endowment money also have expressed fears that Curran, with his master's degree in English and brief but stormy tenure at the National Institute of Education, lacks the experience and temperament required to preside over the endowment.

"I have nothing personally against Mr. Curran, but his qualifications so far as I know them are unrelated to what is required in the job," said O.B. Hardison, former head of the Folger Library and chairman of the board of the Humanities Alliance, a trade association.

The humanities endowment chairman, say Hardison and others, must oversee an operation responsible for choosing between a profusion of frequently esoteric grant proposals. "All these things require someone who is thoroughly knowledgeable about higher education, and that's not Mr. Curran," Hardison said.

Curran's friends scoff at that notion. "From my point of view that's no handicap, that's a blessing," said Charles Martin, former headmaster at St. Albans School.

Curran, 51, made headlines at the Institute three years ago when he wrote the president suggesting that the agency be abolished. "After seven months here," Curran wrote the president, "I have concluded that the best way to advance your goals is to abolish this agency . . . The taxpayers simply do not need a $90,000 survey on the political attitudes of college professors, or a $37,000 study of the 1973 New York City [school] Board elections."

Curran clashed with his boss, then-Secretary of Education Terrel Bell, who friends say did not know about the letter until after Curran sent it. Curran resigned shortly after, ending a tenure that had made him the darling of conservative publications and columnists.

The Institute -- the research arm of the Department of Education -- has been a target of conservatives who have charged it with a bias toward liberal research. Curran terminated a number of longtime research contracts and advocated proposals to study conservative themes including tuition tax credits for private schools.

His stint at the Peace Corps has been stormy, too, according to acquaintances who say he has disagreed with Peace Corps director Loret M. Ruppe on agency policy. "He's not a compromising fellow when he's morally certain that something is true," said Eugene Del Gaudio, executive director of the conservative Public Advocate group.

Friends say, however, that raising a ruckus is not the traditional Curran style. At the National Cathedral School, where he served as headmaster from 1968 to 1980, he is remembered as an able administrator who steered the school safely through the turbulence of the late '60s and early '70s, liberalizing the curriculum and abolishing the dress code.

In 1980, the Massachusetts-born Curran headed a political group called Professionals for Reagan. According to friends, he is a friend of Vice President Bush, whose family he became acquainted with during his early academic career in Texas. "They shared babysitters," says a friend.

The National Endowment for the Humanities is a federal agency with an impact and visibility far greater than its relatively small $140 million budget, and the periodic search for its chairman usually produces political fireworks. Former president Jimmy Carter once complained that finding a chairman for the humanities endowment was harder than finding someone to run the Department of Defense.

The endowment awards thousands of grants and fellowships to scholars, museums and universities for research and preservation. The chairmanship has often served as a pulpit for administrations' views on the role of liberal arts scholarship in American life.

Reagan appointee Bennett, for example, used the endowment to call for a return to the study of the classics of western history, literature and philosophy. Critics and admirers agree he has steered the endowment away from the cultural pluralism that marked the Carter years.

Curran has declined to comment on the chairmanship, but friends and associates on both ends of the political spectrum take issue with the notion that his credentials, political philosophy and personality are inadequate for the job.

"He's no dyed-in-the-wool conservative," said St. Albans' Martin. "He's a very moderate person, and very easy to live with."

Leaders of numerous humanities groups, while conceding that they do not know Curran personally, say they fear he will be too ideological for the job. That, and not Curran's credentials, they say, is the real objection to his nomination.

"To some extent the real question is: are we looking for someone who will treat the NEH as a means of encouraging fine scholarship in a wide number of areas or someone who will treat it as a moral mission to tell us all what is great and noble in American and western heritage?" said Joseph Duffy, chairman of the humanities endowment during the Carter administration and now chancellor of the University of Massachusetts.

According to administration officials, some of the leading alternatives to Curran include Charles Ritcheson, a history scholar and head of the library system at the University of Southern California; William Allen, a prominent black Republican and professor of history at Claremont College in California; Gertrude Himmelfarb, a scholar, and wife of neo-conservative theoretician Irving Kristol; and Robin Winks, a history professor at Yale University and former cultural attache' at the U.S. embassy in London.