In a showdown at the candidate's Los Angles home Nov. 26, John Sears won total control over Ronald Reagan's last try for the presidency -- an event that reflects past struggles and will shape the future of the Reagan campaign.

It boiled down to "him or me" between Sears and Reagan's closest longtime aide, Michael Deaver. Two other senior campaign operatives present supported Sears, and Reagan did not back Deaver. It was then that Deaver, having devoted a decade in service to Reagan -- and every waking day the last five years to electing him president -- offered to quit. The offer was accepted.

Deaver follows a trial of other longtime Reagan servitors tossed over the side by their chief in the belief that Sears, a relative newcomer to Reagan's inner circle, knows best how to put him in the White House. That suggests Reagan, whose nice-guy image dates back to his Hollywood roles, is a harder man than generally known.

Sears has been softening Reagan's right-wing image, but hardly anybody disagrees with that. The significant point is that the Reagan campaign now is run by men owing primary allegiance to Sears, not Reagan. Sears, whose press interviews have been eclipsing Reagan's, controls not only strategy and issue research but vital channels to the candidate. In sum, it is today John Sears' campaign.

That hardly seemed possible early last year when Sears, an urbane Washington lawyer, was under fire from California Reaganites for his management of Reagan's near-miss 1976 campaign. Behind his self-assured exterior, Sears was worried. He told his bright young deputies -- Jim Lake, Charles Black and David Keene -- they should come as a package. If Sears got bounced, all four should join another campaign. (In fact, Keene joined George Bush's campaign, partly because he doubted Sears' staying power with Reagan.)

The doubt was whether anybody could overcome Lyn Nofziger, seldom far from Reagan's side for the past 15 years and determined to displace Sears for 1980. The tough-talking, fast-punning Nofziger had the nation's grass-roots convervatives on his side, but he finished a poor second in the Byzantine political games played around Reagan.

One reason Nofziger was demoted to semi-menial jobs and eventually left the campaign was covert support for Sears from Deaver, partner in the Deaver-Hannaford public relations firm that has managed Reagan's affairs since he left the governorship. But amid offstage cackling by the defeated nofziger, Deaver found the tables turned.

On Nov. 26, the Deaver-Sears struggle had reached a point requiring Deaver to confront the candidate. Arriving at Reagan's home in Pacific Palisades, he found Sears, Black and Lake ahead of him -- and united against him. Sears prevailed, a press release was hurriedly prepared and Deaver hastened to a northern California duck hunting trip -- far away from the prying press.

That clinched it for Sears. Two weeks earlier, Dr. Martin Anderson quit as full-time research chief to return to Stanford University. Even before Anderson's decision, the effective research operation had been transplanted to Washington under Sear's direction -- a hidden reason for Anderson's departure.

With Pete Hannaford having decided long ago to return to the Deaver-Hannaford firm, that left one holdover from Reagan's Sacramento days: Edward Meese, chief of staff during Reagan's second term as governor. Distraught over Deaver's fall, Meese flew the red-eye to Washington that night and huddled with the campaign's nominal national chairman, Sen. Paul Laxalt, the next morning.

Meese's trip fit a previously planned Washington visit, and he is not quitting as issues adviser traveling aboard the candidate's plane. But with the research machinery in Sear's hands, Meese is no rival. Indeed, plans are afoot to move national campaign headquarters to Washington -- symbolically affirming Sear's triumph over the Californians.

The time and effort consumed in that triumph may explain why Reagan's long-awaited campaign inaugural Nov. 13 seemed ill prepared. With the fight finished, some insiders fear a one-man stranglehold over the campaign. Outside consultants complain they cannot penetrate the Sears screen. "I never thought I had a problem with John," one adviser told us, "but John apparently had a problem with me."

Sears is the toast of American politics, managing a nearly errorless frontrunner's campaign while decapitating his rivals. But he wins no applause from hitherto ruggedly loyalist Reaganites who are coming to view Bush as a viable alternative. To keep their support, Reagan may have to show by word and deed that this presidential campaign is his own, not his manager's.