While Ronald Reagan embarks on a Mexican vacation, his campaign staff is working overtime to convey the impression of an on-the-job, analytical candidate who is devoting his full attention to the problems of the presidency.

Reagan and his wife, Nancy, left today with two other couples for a five-day vacation at the plush south-of-Nogales ranch of a milionaire Los Angeles investment counselor, William Wilson. The Republican presidential candidate's presence remained at home through the medium of a series of paid radio speeches the Reagan campaign launched today on the CBS network.

The first broadcast, on "Leadership and the Presidency," quoted from two former presidents named Roosevelt, listed attributes that Reagan said are needed in an American president and asserted that "speaking out for defense for our nation is not a sign of militarism, but sound common sense."

On Thursday, in Los Angeles, Reagan chief of staff Edwin W. Meese and domestic issues advoser Martin C. Anderson will announce some new advisers and discuss the formulation of domestic policy.

And on Sunday, foreign policy adviser Richard V. Allen and campaign director William J. Casey will return from a five-day visit to Britain and France where they were to hold private meetings with journalists, scholars and members of Parliament. The scheduled high point of the trip, which replaced a now-canceled visit by Reagan to Europe, was a private meeting with British Prime Minster Margaret Thatcher.

Reagan is an admirer of the Conservative Party prime minister, whom he views as a political success and a good omen for his own candidacy.

These various activities by Reagan aides come at a time when the candidate himself is doing nothing of a public nature.

After Reagan returns Monday from the Wilson ranch, he will spend the week before the Republican convention at his Pacific Palisades home. He has a midweek interview with Mike Wallace for "60 Minutes" but no scheduled public appearances until he arrives in Detroit on July 14,

Reagan is known to believe that he needs and deserves a vacation after the grind of the Republican primaries. But there was a flutter of concern in his campaign this week that the 69-year-old candidate might be perceived as fueling stories about a "nine-to-five" approach to the presidency if he takes too much time off from the campaign.

Accordingly, Reagan press secretary Ed Gray said today that the Mexican vacation was actually "a retreat" at which Reagan would work on his convention acceptance speech and ponder his choices for vice president. Gray called the speech and the selection of a running mate "two of the most important actions Reagan will make during the campaign."

The prevailing view in the Reagan camp is that the vice president will be choen from a five-man field -- former ambassador George Bush, Sens. Howard H. Baker Jr. of Tennessee and Richar Lugar of Indiana, former treasury secretary William E. Simon and New York Rep. Jack Kemp. There has ben occasional mention of Donald Rusmfeld, a former Illinois congressman and NATO ambassador who served as chief of staff under President Ford.

In his radio address today, Reagan outlined seven desirable attributes for a president, among them "the capacity to identify, analyze and adapt to changing conditions in the nation and the world, the courage to make what at first may seem to be unpopular decisions but ones based on an understanding of national needs and, finally, the willingness not only to admit error, but also to learn from it.

"A president with these attributes doesn't have to say 'Trust me,' as if all the people should do it put their faith in him and hope for the best," Reagan said.

The speech was written by Peter Hannaford, a longtime adviser who is associated with the Los Angeles public relations firm of Deaver and Hannaford.