Senate action on President Reagan's controversial nomination of Thomas W. Pauken to head Action, the federal volunteer agency, has been postponed until next week because of a dispute over Pauken's service as a military intelligence agent during the Vietnam war.

The controversy pivots on the Longstanding policy of the Peace Corps, a branch of Action, of rejecting anyone with certain intelligence backgrounds in order to protect its personnel abroad from allegations of spying.

Pauken argues that the policy is irrelevant since under a two-year-old executive order the director of Action has virtually no control over Peace Corps policy or operations; Action has control over Peace Corps recruiting which is at the heart of Pauken's opponents' concern. He also testified in his confirmation hearings that his "principal work in the [Mekong] Delta was involved as an analyst."

However, The Washington Post has learned, and Pauken now acknowledges, that in Vietnam Pauken was "a case officer" assigned to run a network of South Vietnamese agents. These new details come as Congress is moving to consider legislation completely separating the Peace Corps from Action before further considering Pauken's nomination.

In interviews with The Post, two of Pauken's former colleagues in the Delta who also served as province intelligence officers at the time painted a different picture than Pauken did in his testimony.

David G. Wilson, now a Washington lawyer and a friend of Pauken's, and another former colleague of Pauken who insists on anonymity say that a province intelligence officer was really a "case officer" or "an agent handler," whose duties would include managing and training a several-tiered network of agents who would report back information on Vietcong troop movements and plans.

"In practice, we were handling the people doing the spying," Wilson said.

"Our duties included reviewing agent assets, dispatching agents or intelligence gathering missions, recovering the agents after the mission debriefing them and reporting back their intelligence to operational units," the other colleague said.

Several officers who served with Pauken including one of his former commanders, Col. Thomas S. Mayberry (ret.) said that a province intelligence officer's duties would include contact with other U.S. intelligence agencies operating in the province, including regular contact with the CIA agent in the area, and passing on information to the local representative of the Phoenix program.

In an interview, Pauken continued to insist that he had no contact with the CIA in the Delta, but acknowledged that for his first three days in the field he was assigned to a program to train Vietnamese case officers to manage networks of intelligence agents before the program was agents before the program was abruptly terminated. He was then assigned to another province to operate his own network of informers, with whom he dealth through an interpreter.

Pauken says, however, that his first act was to shut down the operation of a paid Vietnamese informant who "had been around long enough to con us out of enough money to start a chicken farm."

His duties were covert, he says, only in that Vietnamese civilans did not want it known that they were reporting Vietcong movements to Pauken's interpreter in return for occasional cash payments.

Pauken says he appreciates the concern of Peace Corps volunteers that these are precisely the sort of activities of which they are often falsely accused. But he does not feel that his own background constitutes a bar even if he were nominated to be director of the Peace Corps, rather than Action.

A self-described 1960s activist who organized college demonstrations supporting U.S. involvement in Vietnam, Pauken served for three years in Army Intelligence. He then moved along the periphery of Republican politics as a former deputy director of the White House Fellows program, a two-time losing candidate for a Dallas congressional seat, and the narrator of a conservative film attacking the "leftist" political designs of Jane Fonda and Tom Hayden.

"If I were a leftist, given whay they have done to me -- pulling my military records without my permission, what would civil libertarians say then?" he asks.

"They" are Senate minority whip Alan Cranston (D-Calif.) and his staff, and "what they have done," according to Pauken, is to persecute him for his record of military service in Vietnam. Leftist McCarthyism, Pauken calls it.

"Mr. Pauken's complaints are red herrings," Cranston responded. "The sole and only issue is that his intelligence background could jeopardize the lives and work of Peace Corps volunteers and staff overseas and undermine the effectiveness of the entire program."

Cranston wants to remove even the appearance that the Peace Corps is under the control of a former intelligence officer, which he considers as dangerous to volunteers as the reality. On Wednesday, he secured an agreement in the Senate postponing consideration of Pauken's nomination until next week by which time the Senate Foreign Relations Committee will have taken up a Cranston-sponsored bill to separate the Peace Corps totally from its parent agency, Action.

The House is expected to consider a similar bill next week to be sponsored by Rep. Clement J. Zablocki (D-Wis.), chairman of the House Foreign Affairs Committee. Two years ago the House, led by conservative Republicans, voted overwhelmingly to separate Action from the Peace Corps. If the bill clears both houses aides to Cranston said yesterday that he would drop his opposition.

Now the White House feels it cannot bow to Cranston's challenge. According to two administration sources, the White House will oppose Cranston's bill and push for Pauken's confirmation.