The internal aspect of the current demolition campaign against Zbigniew Brzezinski is illuminated by a secret mission on Capitol Hill two months ago by Richard Moose, assistant secretary of state for African affairs.

On April 24, Moose visited the office of Rep. Charles Diggs (D-Mich.), chairman of the House African affairs subcommittee. His purpose, according to a memorandum written that day by Moose, was "to discuss with him (Diggs) the possibility" of aiding anti-Soviet guerrillas in communist Angola.

In the intervening two months. State Department officials have planted a multitude of news accounts blaming Brzezinski for trying to resume U.S. interven in Angola's continuing civil war. Never has there been one suggestion that Moose, a focal point of anti-Brzezinski attitudes in the State Department, was engaged in exactly the same activitiy, he was because it was then an official administration initiative.

Angolan policy has focused an intensifying barrage against Brzezinski, the president's national security adviser, from multiple sources: Moscow, Havana, the Senate and news media, plus undercover encouragment from within the State Department and the White House.

Brzezinski's problem transcends Angola and Africa. The campaign against him did not start until his proposed tougher policy toward Moscow became obvious. Since then, he has been the target of the relentless verbal assault often heaped during the past 30 years on U.S. officials with anti-Soviet inclinations.

But because that assault has been sustained by insinuations that Brzezinski has adocated madness on the African continent, it is worth tracing down the abortive change in Angolan policy. It began at an April 7 meeting of the Cabinet-level Special Coordinating Committee (SCC), which decided to explore helping Lucas Savimbi's UNITA forces fighting the Cuban expeditionary force in Angola. A subsequent SCC meeting decided to approach key members of Congress.

Visits to the Hill for that purpose by CIA Director Stansfield Turner, Brzezinski and David Aaron, Brzezinski's deputy, have been widely reported. What was not made public was the simultaneous visit to Diggs by Moose, considered by his colleagues to be the State Department's staunchest foe of calling the Kremlin to account for its African adventures.

Moose's memo, classified secret, described the visit in some detail. He asked Digg's opinion of providing "non-lethal" aid to "stiffen UNITA's resistance" and encouraging assistance from other countries, all to make the Angolan caper "more costly" for the Cubans. Moose's memo has no critical overtones and seems moderately enthusiastic.

To nobody's suprise, Diggs put his thumbs down. "That's how we got involved in Angola in the first place," the congressman was quoted by Moose as saying. With similar responses elsewhere on the Hill, the SCC initiative died without ever getting to the president. Brzezinski soon was publicly depicted as the author of Angola reentry, and the campaign against him was on.

A softer path in Africa quickly followed in Secretary of State Cyrus Vance's June 20 speech in Atlantic City. State Department officials, having a month earlier predicted Vance would be forced out by Brzezinski's preeminence, now happy whisped that the secretary had refused to remove phrases in the Altantic City speech that might offend Brzezinski. Ambassador Donald McHenry was dispatched on a peace mission to Angola, reversing the pro-UNITA initiative laid out April 7.

Contrary to many published accounts, the State Department lost its fight to give McHenry authority to promise Angolan President Agostinho Neto that the United States would discourage other countries from aiding Savimbi's UNITA. Brzezinski therefore at least prevented a total U.S. sellout of one African fighting force opposing Soviet-Cuban expansionism.

But there is no doubt that the McHenry mission was a severe setback for both Brzezinski's policy and his own status. It gives credence to the ridiculous image of the national security adviser (newly identified in all news accounts as "Polish-born") driving the president into dangerous confrontation with the Kremlin over obscure African intrigue.

White House insiders claim the assault on Brzezinski only strengthens the president's support for him. Why, then, did not President Carter takes Brzezinski off the hook by revealing the SOC Angolan intiative and State Department participation in it? For the simple reason that he did not know about it, say reliable officials. In other words, what is happening to Brzezinski could happen only in this strange administration.