Anyone who has ever applied for a new job knows that the interview is a crucial, and often decisive, part of the process. And anyone who follows politics knows that interest groups will do whatever they can to influence the choice of a high-ranking executive-branch official in a position of particular importance to them.

The Reagan administration recently encouraged conservative groups to combine these aspects of political patronage in a way that can only increase the power of special interests to set the public agenda.

Last week several conservative political groups "interviewed" two leading candidates to replace Terrel Bell as secretary of education. According to reports, the groups asked the White House for permission and were allowed to proceed.

So Bill Bennett, director of the National Endowment for the Humanities, and John Silber, president of Boston University, were interviewed by a group of conservative activists and congressional staff. A third candidate often mentioned for the job, Office of Personnel Management Director Donald Devine, was not interviewed and is no longer a "serious candidate."

Involving outside groups in the selection of politically appointed officials is not new. The American Bar Association reviews the credentials of candidates for nearly all federal judgeships, including the Supreme Court. After a review, the ABA offers one of four rankings: "unqualified," "qualified," "well qualified" and "exceptionally well qualified." Only rarely does the ABA actually meet with the candidates; the review is confined to written materials and interviews with individuals who know them. Moreover, the review is confined to the candidate's general fitned judicial temperament. It is not a political litmus test.

Special-interest groups need not worry about general fitness or temperament; they can focus on the details. For conservative groups in education, this probably means school prayer, tuition tax credits, discipline, vouchers and other items that Secretary Bell did not pursue with sufficient enthusiasm.

Like most things in politics, this has its lighter side. To anyone who knows them, the thought of such distinguished and strong-willed individuals as Bennett and Silber trooping off, r,esum,es in hand, to be interviewed by congressional staff and political ideologues has a theater-of- the-absurd quality to it. (So strong is Silber's personality that his stormy tenure at Boston University was the subject of a Mike Wallace story on "60 Minutes.")

But formal screening of executive appointments by special interests raises serious issues. Changes of this kind become institutionalized very quickly. Giving one narrowly focused interest group special access and the imprimatur of the White House will lead to similar demands from other groups. Tobacco farmers will expect this courtesy the next time a secretary of agriculture is chosen, and business groups will probably want to interview candidates for the next secretary of commerce.

And these procedures, once formalized, get passed from one administration to another. New Right groups that are happy to have a hand in picking Bell's successor may one day have to contend with Ralph Nader interviewing candidates for the Consumer Product Safety Commission or, heaven forbid, the National Education Association quizzing a potential secretary of education about how he or she would increase federal funding and influence.

Moreover, such an approach will make it harder to recruit talented men and women for federal service. The honor of being asked to serve the public is, for some individuals, now outweighed by the financial sacrifice and the loss of personal privacy. Adding the need to be approved by political activists may provide another reason to refuse.

Secretary Bell has indicated that sniping from the New Right contributed to his decision to resign. Indeed, he expressed "amazement" when told about the interviews. He said, "Certainly conservatives should have some input, but I hope they won't be the only ones. . . ."

But the basic question is simply one of leadership. Who should take the lead in selecting appointed individuals to run government agencies: an elected president and his assistants, or self-appointed guardians of a narrowly conceived political agenda?

During the 1984 election, Walter Mondale said that Jerry Falwell would be choosing Supreme Court justices if Ronald Reagan were reelected. The White House, of course, angrily denied the charge and promised that outside groups would not have excessive influence in the selection process. It remains to be seen if this experience is a sign of weakened resolve.

Formal screening of executive appointments by interest groups is not a conservative idea; it is a radical and pernicious one, wholly inconsistent with our long tradition of independent appointment by the chief executive. There is only one body with the power and responsibility to approve executive-branch appointments: the Senate. To share, however casually, that authority with special-interest groups compromises the appointment process.

Courtesy calls to well-placed and important constituencies are part of the ebb and flow of Washington life, but vetting by narrow special interests is not. It comes dangerously close to giving special-interest groups a veto over executive appointments.