To the outside world, Michael Horowitz may look like another conservative activist in the Reagan White House -- a former Democrat, a neoconservative whom movement conservatives now consider "one of us." But Horowitz sees himself as a civil rights activist for all seasons.

He was recruited into political life by the ultimate liberal organizer, the late Allard Lowenstein, and sojourned during the 1960s at the University of Mississippi, where he taught civil rights law. When he returned home to New York City, the "disquiet at the literal madness I saw" prompted a crisis of belief. He eventually reacted by registering as a Republican. For months after abandoning the party of his fathers "I hardly felt Jewish," he wrote in an article in a Republican Party publication.

In that confessional piece, "Why I Am a Republican," Horowitz touted an obscure Michigan representative named David Stockman as "soon to be ripe for national leadership." Stockman and Horowitz were later drawn together by mutual admiration. With Reagan's election, Horowitz's prophesy came true, and he found himself appointed as the counsel to the new director of the Office of Management and Budget.

As a liberal, Horowitz was voluble, passionate and utterly committed. Now he has put those qualities in the service of the Reagan administration, railing against programs he believes abuse the poor -- affirmative action, the Legal Services Corp. and the War on Poverty. Within the administration, Horowitz became a key player in the network of those who have slid across the political spectrum and are known as neoconservatives. These disillusioned intellectuals specialize in ideological argument, published in journals such as Commentary.

After Reagan's 1980 victory, some neoconservatives left the realm of ideas for government, where they would test their theories: Jeane J. Kirkpatrick, for example, left the American Enterprise Institute to become the United Nations ambassador.

The most influential neoconservative of all may well be Richard N. Perle, who was an aide to Sen. Henry M. Jackson and later appointed assistant secretary of defense for international security. He heads a network of hard-line defense specialists drawn from Capitol Hill and now lodged in the Pentagon, adamantly opposed to all past arms control agreements with the Soviet Union. Inside the administration, Perle's office is considered among the most dogged and effective, and Perle himself has had great personal influence on defense policies.

In spite of their conversions to the right, the neoconservatives are not fully accepted by many within the conservative movement. "Most of their work is in foreign policy," said a conservative administration official. "There's still concern about their overall philosophy. Kirkpatrick is a perfect example of that. In a quiet conversation conservatives will say, 'Do you know where she stands on domestic issues, on education and social issues?' Mike Horowitz is a kind of an exception to the rule. People in the conservative movement had to get to trust the neoconservatives."

On July 19, 1982, Horowitz circulated a private memo among top administration officials advocating more conservative appointments as part of the solution to Reagan's political troubles that summer. "All of the managerial skills in the world," he wrote, "complete loyalty to the president and impeccable Republican credentials will not give the president what he needs . . . As the political struggles in which the administration is engaged are rooted in and played out in the world of ideas, it becomes all the more important for appointees to be men and women of and with ideas."

In an interview, Horowitz reflected on the neoconservatives' ordeal of assimilation into their new political milieu. He mentioned a young couple, both intellectuals and born-again Christians, who have held important administration jobs. "They don't go through the trauma I did," he said. "They come to it so clearly and neatly."