Ronald Reagan's top adviser today dismissed the idea that Reagan is not in charge of preparations for his presidency and said the president-elect will begin a series of policy meetings with his Cabinet in Washington the first week of January.

Edwin Meese III, whose title will be counsel to the president, was as coolly confident at today's news conference as at every other public appearance as chief spokesman for the new administration since the election, but the tone fo the questions and answers reflected how things have changed since Reagan's landslide victory six weeks ago.

The Reagan administration is not yet in power, but enough decisions have been made that there is a record to question. Enough choices have been narrowed to make some groups unhappy.

Meese was asked repeatedly what Reagan, who has been secluded in his Pacific Palisades house except for brief outings to run errands and see friends, is doing.

"What he is doing is really running things," Meese said. "He's making decisions . . . he's reading memoranda."

One reporter pointed out that Reagan seemed not to know yesterday whether he was going to visit Mexico before the inauguration. A Jan. 5 meeting with Mexican President Lopez Portillo in Juarez was announced a few hours later.

"Oh, c'mon . . . of course he did [know]," Meese said. He said Reagan had known of the Mexican trip some time ago, but had only learned of the exact timing yesterday.

"He's taking a very active role. He's totally cognizant of all the things that are happening . . . and obviously he's making all the decision," Meese said of Reagan.

A series of questioners asked whether Meese considered it politically unwise to have named Jackie Presser, a Teamsters vice president from Cleveland, as an economic adviser to the transition team. Presser has been rumored to have ties to organized crime.

Meese didn't back off an inch.

"It was desirable to have someone with that background on the transition team," he replied. The Teamsters were the first and most important union to endorse Reagan for president.

"Not only has he never been convicted, he's never been indicted not even subpoenaed," Meese said.

The Labor Department has filed a civil suit against Presser, but Meese said that is not significant.

"The government is no more reliable than any other plaintiff," he said. Then he added: "We expect that to change after Jan. 20."

Meese said that declaring an economic emergency is one of the possibilities the Reagan team is contemplating. He was asked whether such a declaration would include dramatic presidential actions like Franklin D. Roosevelt's closing of the banks in 1933.

"It's entirely possible that there may be some executive orders. I don't contemplate anything as drastic as closing the banks or even closing the stock exchange," Meese said.

Executive orders that might be issued would involve freezing hirings, controlling federal spending and limiting government borrowing, he added.

Meese said that Donald Regan, the nominee for treasury secretary, would be the administration's chief spokesman on general economic affairs.

On two other matters, Meese indicated that changing times have altered Reagan's thinking.

Shortly after the election, Meese said that Reagan would reduce the size of the Cabinet by stripping Cabinet rank from some officials who are not department heads. He cited the ambassador to the United Nations as an example.

Meese said today he doubts that the U.N. ambassador will be excluded from the Cabinet.

During the campaign, Reagan reversed an earlier position and came out in favor of the federal bailout of Chrysler. Meese said that "at this point we haven't taken a policy position" on whether federal aid to Chrysler should be continued. He said that. Chrysler's continuing troubles and appeals for large fresh sums created new circumstances which the Reagan team would have to consider.

Meese made these other points:

Alexander Haig will have no problem winning confirmation as secretary of state. "The only question is whether the Democrats, for reasons of their own, will make a lengthy deal of it."

Possible deployment modes of the MX missile will be thoroughly reviewed by the new administration, including modes that would have been prohibited by the strategic arms limitation treaty (SALT II) signed by President Carter but never approved by the Senate.

The meeting with the Mexican president before Jan. 20 "indicates the importance that the president-elect gives to our relations with Mexico." Mexico will be treated as "a true partner."

Reagan was willing to make a similar brief trip to Canada before his inauguration but scheduling problems on the Canadian side made it impossible.

As president, Reagan will meet regularly with the press. "A valuable purpose is served by the president meeting with the press on a regular basis."

Meanwhile, transition press spokesman James Brady in Washington downplayed talk that Reagan might declare an "economic emergency." He said James A. Baker III, who has been designated chief of staff in the Reagan White House, now says he used words that were "too strong" when he indicated Wednesday that the matter was being given serious consideration.

"The economic emergency declared itself," Brady said at a luncheon with reporters, noting that Reagan has been campaigning for months against the Carter administration's economic policies. "You have to be careful not to build a frenzy" over the issue, or unnecessarily raise expectations.

"The economy isn't going to turn around overnight," he said.