John P. Sears, the spurned Machiavelli of Republican politics, yesterday drew a portrait of Ronald Reagan's campaign as an operation plagued with incompetence, internal rivalries and an indecisive candidate, unprepared on the issues and insulated from the problems on his staff.

But Sears said he still supports Reagan for president and doubts that he will go to work for one of Reagan's rivals.

The picture he drew of the Reagan campaign was, perhpas, self-serving. It blamed the failings of the campaign on anyone but the man supposed to be in complete command -- Sears himself.

But Sears, who was fired Tuesday as executive vice chairman of the campaign -- along with press secretary James Lake and national political director Charles Black -- confessed in a news conference at the National Press Club that he was never fully in control.

Instead, he said, Reagan relied on a group of old friends who would endrun Sears. "The operation always suffered from a degree of disorder because people felt they could talk to the candidate directly and unilaterally. bEvery day, you would find yourself catching up," he said.

Reagan, Sears said, was told about the financial and personnel problems, and the need for better briefing on issues, but did not act. Reagan "is a very kind human being . . . who should be harder" on his staff, Sears said.

Sears said that he felt from the beginning that Reagan "was the best man to be the Republican nominee and that's still my position . . . Ronald Reagan is the kind of man whom people could believe in as a strong president. Whatever our relationship has been is not really relevant."

Sears said he will speak to other Republican candidates but I "don't expect the circumstances to change."

The three aides denied that their description was an indictment of the candidate's ability to govern. "You can examine any other presidential campaign and you'll find worse problems," Black said.

The hour-and-a-half-long press conference was a difficult ordeal for Sears, Black and Lake, who had come so close to helping Reagan get the nomination four years ago and now found themselves out in the cold. But they spoke calmly and quietly under the television lights. The only sign of emotion was Sears' hands, trembling as he lit a cigarette.

Although Reagan claimed that Sears resigned after being offered a reduced role in the campaign, Sears said yesterday he was fired without being offered another job. All three men told of being called into a meeting with Reagan, Nancy Reagan and New York attorney William Casey, and being handed a press release saying that all three had resigned.

"That's a euphemism for being fired -- make no mistake about it," Lake said. He and Black said they still support Reagan and will not work for another candidate.

Casey is replacing Sears as executive vice chairman of the campaign. However, the principal power struggle of the campaign was between Sears and San Diego attorney Edwin Meese III, a Reagan intimate, who will now run the campaign along with Casey and several others in a less hierachical arrangement.

Sears denied that he was fired because Reagan's campaign has overspent, or because there was any disagreement over political strategy or ideology.

Meese, he said, had been responsible for the budget until September but "didn't really have a budget" which was finally put together by Lake at the end of the year.

He blamed long-time Reagan aide Lyn Nofziger for the failure of a direct-mail fund-raising operation which netted, he said, only 50 cents per $1 spent. He blamed another Reagan staffer, Michael Deaver, for authorizing above-budget expenditures on three concerts and the announcement dinners.

The result, he said, was $2 million worth of expenditures that were charged against the campaign limit. Nofziger and Deaver were forced out of the campaign last fall largely, Sears said, because of these financial problems.

Sears also criticized the "casualness" of the campaign toward briefing the candidate on issues -- Meese's responsibility since September. "I have not always been sure [Reagan] is adequately briefed on matters of substance for which people hold him to account," Sears said.

That was one reason Sears said he preferred not to have Reagan debate the other candidates in Iowa -- a decision that many feel cost him votes. However, Sears said it was Reagan's decision -- not his -- not to participate in the debate.

Sears said he first learned that he, Black and Lake were to be fired by unintentionally overhearing a conversation between Meese and another staffer three weeks ago. He said he "reflected on that for a time" and then "sat down and discussed this with Mrs. Reagan.

"I am a great believer that during a campaign you must never bother the candidate . . . when his attention should be directed toward winning votes, because he might be distracted."

On Feb. 15, Black and Lake also went to Nancy Reagan to propose that the personnel conflicts be resolved by putting Casey in charge of issues and policy over Meese.

Lake said she never got back to them until the meeting at which they were fired.

All three aides rejected the interpretation that the campaign disputes are ideologically based. "A number of people in the country perceived that there were two groups in the operation, one more strongly conservative than the other," Sears said. "That was never the fact."

Black, known as a staunch conservative, said, "We never had any ideological differences within the group or serious differences about strategy or tactics. We all agreed." He added that anyone who has ever tried to change Reagan's views about anything knows "he would rather not be president than change."

Sears also denied that he was fired because of Reagan's Iowa caucus loss, where his "front-runner" strategy was to campaign moderately and avoid confronting his challengers. Sears said he had always intended to wage a more intense, personal campaign in New Hampshire, where Reagan won overwhelmingly.

Noting that he had personally known some 40 actual and potential presidential candidates, Sears said, "Most men who run for president have a common problem: because they've been in the business of politics so long, in order to get to the point where it is possible for them to consider running for president, they've lost some perspective on what real life is like.

"As they move up the ladder and get closer to being president, whatever it was that was overpowering about them when they first started in politics and did well, gets diminished."

However, Sears said Reagan "has got a clear perspective about himself. He does not suffer from that anomoly and that in itself makes him a good candidate to be president. . . . It does no good to sit and talk about anyone's failings. The country must vote for what is objectively good in someone they see and hope that good is definitely there.

"I'm supposed to have a reputation as a coldblooded politician, but I've been in this business 15 years and I can tell you this particular election is more important than any I've seen before."