President-elect Ronald Reagan has decided to endorse Utah conservative Richard Richards for the chairmanship of the Republican National Committee, according to sources.

Such an endorsement would virtually assure the election of Richards, the three-time state chairman of the Utah Republican Party, who has emerged in the last few days as the overwhelming favorite of the Reagan high command.

RNC Chairman Bill Brock, whose more moderate politics have earned him little support within the Reagan inner circle despite his leadership of the nationwide Republican sweep in November's elections, had hoped to be named to a top Reagan administration post -- either secretary of commerce or undersecretary of state. But according to sources, Reagan so far has offered only less appealing jobs: the ambassadorship to the Organization of American States or a deputy ambassador's post at the United Nations.

The selection of Richards as national chairman must be formally decided by a vote of the Republican National Committee when that group meets sometime before Reagan's inauguration Jan. 20. But party sources said that Reagan's choice is sure to be honored by the national committee.

The selection of Richards, who had served as western coordinator for Reagan's campaign this year, was the culmination of a power struggle of sorts within the Reagan inner circle.

Sen. Paul Laxalt (R-Nev.), Reagan's campaign chairman and one of his closest advisers, had favored the chairman of his home-state Republican Party, Frank Fahrenkopf, for the post. Fahrenkopf's list of credits included his serving as attorney for singer Wayne Newton, but apparently neither that nor Laxalt's backing was enough to convince other members of the Reagan inner circle.

Instead, Reagan's campaign pollster, Richard Wirthlin, his White House counselor-designate, Edwin Meese, his former press secretary and future political adviser, Lyn Nofziger, and his long-time close adviser Michael Deaver, all were said to have come down firmly in support of the 48-year-old Richards.

Republican Party sources said these members of the Reagan camp were concerned that Laxalt would have a dominant influence within the Republican Party if Fahrenkopf got the job, and they apparently persuaded the president-elect to support Richards. Laxalt informed Fahrenkopf Monday that Richards was Reagan's choice for the job, Republican sources said.

"When the weight came down, Paul decided that Richards would be okay," said one source who has talked with Laxalt about the affair.

In 1977, Richards had been Reagan's choice for the Republican national chairmanship. But Reagan then was only a former California governor; his decisions were not held in the partywide esteen they are now, and thus Brock got the job.

Richard's political colleague in Utah, Willian A. Stevenson, the current state GOP chariman, described him as a loyal party conservative. "Dick is a conservative . . . a Reagan-Goldwater type of Republican," he said. "I think you're going to see a nuts-and-bolts type of politician."

Richards said yesterday that he had not received "official word" on whether he had been chosen by Reagan to head the GOP. "I've sort of worked my way up through the ranks," he said, reflecting upon his party career. "And now I'm just waiting."