The failure of John R. Norton III, a wealthy conservative farmer from Arizona, to win Senate confirmation as deputy secretary of agriculture is becoming one of the political mysteries of the year.

More than a month ago, the Republican-controlled Senate Agriculture Committee approved the nomination by President Reagan and whisked it to the floor, where confirmation seemed certain. But there the nomination stopped cold and that's where the mystery began.

The impasse also leaves the GOP with egg on its face. The confirmation roadblock apparently was erected by a Republican senator, said to be miffed about an unrelated matter, and the department's No. 2 official is on the job without the full authority of office.

Ordinarily, Democrats might be expected to object. But that is not the case, even though some, such as Sen. John Melcher (D-Mont.), have asked for details about Norton's income from the department's 1983 payment-in-kind program and about lawsuits involving charges of mistreatment of workers on his farms.

Norton apparently has been blocked by Sen. Mack Mattingly (R-Ga.), who, according to widespread reports, has told the White House that he won't budge until Orson Swindle, also a Republican, is removed from his post as head of the Farmers Home Administration (FmHA) in Georgia.

Mattingly's office refuses to discuss the reports.

George Dunlop, staff director of the Agriculture Committee, said the flap has reached the White House level and he expected it to be resolved with a "promotion" for Swindle. But Swindle, reached in his Athens, Ga., office, said he didn't think he was being promoted anyplace and is mystified about his role in the Norton case.

"Sources tell me the senator is holding up Mr. Norton's nomination until I'm removed," Swindle said. "Last fall, rumors came up that he wanted me out. I talked to him then, but I couldn't get an answer . . . . I've been talked to for two years about going to Washington . . . . I am a great loyalist of President Reagan, but the right job hasn't come up."

Swindle, a former Marine fighter pilot who was a prisoner of war in North Vietnam for more than six years, has a reputation as a tough administrator who aggressively pursues delinquent FmHA loan accounts in Georgia.

"I've done my best to get politics out of the lending business in Georgia," he said. "We've essentially depoliticized the agency and the senator's office has not complained. If I've done something wrong, that's another thing . . . . I feel badly that Secretary John R. Block has to go through these difficulties. And it seems terribly unfair to Mr. Norton, to block him because of another issue."

BITTERSWEET AND STUNG . . . Honey producers soured when the Reagan administration's farm bill proposed to end the honey price support program. But they became absolutely acid-tongued when someone at the Agriculture Department sent out a sample program sign-up form from an imaginary farmer named "Plenty Rich."

"We took it as a slur," said Glenn Gibson of Minco, Okla., president of the American Honey Producers Association, whose 600 members turn out much of the nation's commercial honey. "It was a plus for us in the long run, for it showed an attitude at the department that members of Congress do not appreciate."

Gibson took that and the farm-bill proposal as reason enough to mount a full-scale lobbying effort, which includes a personal letter to Block every few days, peppering him with information on honey and the importance of pollination by bees to American agriculture.

The association argues that beekeepers would go out of business without the support program, hurting all agriculture. But the administration contends that the program is out of whack, having cost taxpayers $88 million to buy surplus honey in 1983 and approximately the same amount last year.

For all his effort, Gibson's letters have produced one direct reply from Block -- a three-line letter apologizing for the Plenty Rich reference -- and a number of replies from USDA underlings. Gibson said he sees about a 50-50 chance that Congress will retain honey supports in some form. "We're not scared," he said, "but we're fighting the secretary, with all the prestige of his office."