Like a troubled theatrical production that tries out new scenes and actors well away from Broadway, the Ronald Reagan presidential campaign is making big changes on the road.

After the third departure or demotion of a major longtime Reagan adviser in as many months, the Reagan candidacy is losing some of its conservative California appearance and taking on the coloration of its pragmatic Washington campaign director, John P. Sears III.

Latest to go was Reagan fund-raiser Michael K. Deaver, who founded the advertising firm that booked Reagan's speeches and distributed his newspaper columns and radio commentaries. Deaver, a key staff aide during Reagan's eight years as California governor, was until his abrupt resignation this week the No. 2 man in the campaign.

Late in August, veteran Reagan aide Lyn Nofziger resigned after disputes with Sears. Two weeks ago, soon after Reagan formally declared his presidential candidacy, issues director Martin Anderson announced he was returning to Hoover Institute in Palo Alto, Calif., and would work only part-time on the campaign.

What made the Anderson and Deaver changes seem all the more significant was that presss releases announcing their campaign roles had been distributed in October. Both men had said publicly that they were "on for the duration" of Reagan's presidential candidacy. A reporter in Little Rock, Ark., where Reagan spoke to a GOP fund-raising dinner Tuesday evening, compared the hurriedly revised Reagan press kit to an edition of the Soviet encyclopedia hastily issued when some Russian leader has fallen from grace.

The Reagan press packet distributed at announcement time Nov. 13 had a list of "key campaign professionals" in which Deaver's biography was given equal space with that of Sears. The list, including a biography of Anderson, was pulled from the packet without replacement within hours of Deaver's resignation.

The result has been that Sears, a 39-year-old Washington lawyer who almost pulled off a Reagan upset of Gerald Ford in 1976, is left in undisputed charge of the campaign.The new people brought aboard as fund raisers and organizers have been chosen or screened by Sears. And all of this seems more than acceptable to Reagan, who makes no secret of his respect for Sears' management skills.

In Los Angeles, shortly before he left on his current campaign swing, Reagan was asked whether Deaver's departure would strengthen Sear's position. Reacting with mild incredulity at the question, Reagan replied: "He's chairman or vice chairman under [Sen.] Paul Laxalt and that's his job and I don't know how you can get much stronger than that."

However, Reagan has sought to play down widespread reports of policy and personality conflicts in the ranks. He observes that Nofziger has become chairman of the Reagan political action committee, Citizens for the Republic. Anderson is aboard the campaign plane, at least for the present trip. Deaver has been given a face-saving appointment as liaison to a committee of busines executives.

One well-placed Reagan insider dismisses the reassignments as "little more than window dressing." He says that while it is true Deaver had business and family conflicts which made it difficult for him to continue with the campaign, the aide also had serious differences with Sears.

This source said the differences, both of style and of substance, came to a head Monday in a meeting at Reagan's Pacific Palisades home. After Sears suggested that Reagan would have to make a choice between him and Deaver, the issue was quickly resolved by Deaver's abrupt decision to resign.

"It's overstating it to say that the conflict is one of conservatism versus pragmatism," this intimate says. "John is conservative on many things and Mike can be pretty pragmatic. But Sears is a national politician with an appreciation for the whole country that many of the Californians lack."

Deaver was not available for comment; Sears said laconically that he "was not surprised" by Deaver's departure.

"It's natural for there to be changes and beefing-up of the campaign as it goes along," he said.

In fact, what has surprised some is not that there have been changes but that they have been so long in coming. Reagan, the widely acknowledged Republican frontrunner, was the 10th GOP presidential candidate to announce for the 1980 race and his campaign has been in the planning stage for nearly a year.

Sears is described by some close to Reagan as the man behind the staff changes, all of which the candidate was reluctant to make.

As governor of California, Reagan, whose reluctance to fire anyone was well known, showed considerable loyalty to his longtime aides. Reportedly, Reagan was slow to ease some of them out of the campaign despite suggestions they could be replaced by better-qualified people. Accordingly, says one initmate, all of the deposed Reagan staffers have been given other assignments or kept on in part-time capacities.

"The key point," says this source, "is that Sears did get what he wanted even though it took him longer than it should have to get it.And we're going to be a better campaign because of it."

Reagan's view, expressed to a reporter at the end of his first campaign trip, is that other than a few political activists and journalists, no one is paying attention to presidential candidates at this point. He said the early start of the 1980 political season and the public's preoccupation with the situation of the American hostages in Iran have worked to divert attention from the various campaigns and campaign-related stories.

With this in mind, both candidate and his campaign manager seem to be treating the early campaign trips as shakedown cruises for testing themes, practicing one-liners and improving local organization.

Whether Reagan will be a better candidate because of the staff changes remains unclear. But it now seems certain that the organization of his 1980 candidacy will bear the clear pragmatic imprint of John Sears, who would rather win with a moderately conservative Republican than lose with one who is perceived as too far to the right.