Despite the stated resolve of President Reagan's senior aides for ending their campaign to cut down Secretary of State Alexander Haig, the continuing deterioration of his position -- aggravated by the White House -- is attested to by two new items of evidence.

Item No. 1: The obscure occupant of a secondary Cabinet office, Secretary of Agriculture John R. Block, publicly fumed at Haig for ignoring him about a French wheat sale to Moscow. The White House did not publicize the fact that although Haig failed to tell Block about the deal, he informed Ronald Reagan.

Item No. 2: Word has seeped out of the White House that among Republican foreign policy heavyweights in regular contact with presidential chief of staff James A. Baker III is Chicago industrialist Donald Rumsfeld, a superb intriguer in many former incarnations, including secretary of defense. That has persuaded one influential Western ambassador that Rumsfeld might soon replace Haig.

The White House campaign to bring Haig to heel in a self-styled "collegial" atmosphere is out of control. Like a whispering campaign, the effort to tame Haig's ambition and limit his power cannot now be stopped by the high presidential advisers who started it. That alarms foreign diplomats here and their home offices, who had hoped for a return to stability in U.S. foreign policy.

What angered Block was week-old word that French Ambassador Francois de Laboulaye had been given a green light March 27 by Haig to sell wheat to the Russians despite the U.S. grain embargo. Block told reporters he was "furious" at Haig and raced to the White House to complain.

In fact, the French ambassador simply informed Haig that France was considering a sale, neither asking nor expecting any response. Word leaked by the Agriculture Department that Haig had failed to inform the White House was inaccurrate. On that same March 27, Haig told the president.

Baker's conversations with Rumsfeld, however innocent in reality, take on a sinister tone in connection with statements coming out of the White House. A senior presidential aide has confided: "We still get this man [Haig] under control." A lesser White House aide predicted to newsmen that Haig would "be gone" by June 1.

The campaign to cut down Al Haig started Inauguration Day when Reagan's senior aides were put out at what they regarded as Haig's effort to grab power over national security machinery. Not, encumbered by institutional memory, they not only blocked Haig but took control themselves, the first time that the White House staff has ever sought to dominate both the national security assistant, now Richard V. Allen, and the State and Defense Departments.

Haig has never recovered, later losing control of crisis management to Vice President George Bush. Friends say the open season on Al Haig limits his effectiveness as a diplomat. One ambassador here blamed anti-Haig incidents, such as Blocks's public attack, for Haig's uneven performance on his Mideast tour. He told us Haig would never have used Israel as the soap box for castigating Syria for "brutality" in the Lebanese conflict if he were not preoccupied with considerations of self-preservation.

Even when Haig makes light of his tribulations, adversaries in the White House stick in the knife. He told a joke on himself at dinner in Jerusalem that was funny enough to be reprinted in full by The New York Times. When one White House aide was asked if he had read the joke he replied, suggestively: "Some important people here didn't think it was all funny."

Haig is not helped by staunch support at every turn from Richard M. Nixon. At the small breakfasts and dinners Nixon now gives at his East 65th Street Manhattan townhouse, he praises Haig, then criticizes the White House staff for taking away the national security portfolio from not only Haig but also Allen and Secretary of Defense Caspar Winberger. Those words get back to the White House and add wind to the whispering campaign against Haig.

To undermine the secretary of state partly because Nixon speaks well of him is as ludicrous as Block's outburst and White House staff predictions that Haig will be controlled -- or else. This trivial byplay so hinders Haig's functioning that in the eyes of the nation's allies, the United States has yet to resume its leadership of the Western world.