Investigations into charges that Nicaraguan rebels commit atrocities or that U.S. aid to rebels in Afghanistan is vanishing might come "later on," but the new Senate intelligence committee will have several other things to do first, Chairman David F. Durenberger (R-Minn.) said yesterday.

Tops on his priority list is "professionalizing" the committee's nine new members and the staff so as to take them out of the newspapers and away from rehashing past mistakes, and to put them into controlling future acts of the intelligence community, Durenberger said.

"If we spend the next two years investigating Afghanistan and the 'contras' [in Nicaragua] we aren't going to get the job done that we are expected to do," Durenberger said in an interview. "These are on the list of things we'll explore later on . . . but the idea that all of us will be in the headline business overturning wrong is not my idea of what the committee ought to be."

Sen. Patrick J. Leahy (D-Vt.), the panel's vice chairman, called last month for a probe of charges that rebels who have been fighting Nicaragua's leftist Sandinista government with U.S. aid for three years have engaged in murder, rape, torture and other atrocities against Nicaraguan civilians.

Sen. Gordon J. Humphrey (R-N.H.) has set up an ad hoc task force of senators and House members to evaluate the way U.S. policy in Afghanistan is being implemented. Humphrey has expressed concern about reports that as much as 90 percent of covert U.S. aid to rebels fighting the Soviet occupation of Afghanistan disappears before it reaches the guerrillas. An aide said Humphrey had hoped that either the intelligence or Foreign Relations committees would look into those reports.

He said as much as $400 million may be involved. "Since the committees are reluctant, we will do it through the task force," the aide said. Hearings are planned later this month.

Durenberger said he is hopeful that other intelligence committee Republicans will support his opposition to renewed Central Intelligence Agency aid to the Nicaraguan "contras." "The program is helping to destroy the [congressional] oversight process" by undermining public confidence in the legitimacy of covert operations, he said. "As long as that little poison remains, we're going to have troubles."

However, Durenberger added, probing the rebels' behavior is another matter. "I'm not real anxious to spend a lot of time being conned by a lot of Nicaragua propagandists" charging rebel atrocities "when I can't get at the human-rights violations by the Sandinistas," he said.

Durenberger added that documenting atrocities probably would be possible but would chart no new waters. "I deplore it, but I predicted it three years ago when this program started," he said.

He acknowledged that Reagan administration officials have asked for alternative proposals for pressuring the Sandinistas to make political concessions. "I said to [former national security affairs adviser William P.] Clark three years ago I wasn't hired to come up with the ideas -- that's your responsibility," Durenberger said.

He has repeatedly made clear his opposition to the Sandinista government, suggesting last month that the administration consider ways to apply military pressure in an overt manner. Several members of Congress have said they may propose withdrawing diplomatic recognition from Nicaragua and passing a law to permit open backing for the resistance forces.

"You have to draft a policy that implements U.S. law," Durenberger said. "If the administration doesn't give us any alternative to the CIA program, there will be serious problems."

Law prohibits the United States from seeking the overthrow of any government with which it maintains diplomatic relations, and bans spending to overthrow the government of Nicaragua.

Durenberger said that, contrary to rumor, he expects to retain most of the intelligence committee's staff and to permit each one to be the "designee" of a committee member. But he said some of the nine new senators will have to accept staff aides as their designees, because "the staff is going to be much more professional and much less honed by the members than it has been."

He said he will expect staff members to labor for the committee 90 percent of their time and keep their senators informed on current issues the other 10 percent, devoting no time to speechwriting, casework or floor statements not related to intelligence activities.

He also said he opposes a pending recommendation from a select committee on Senate reorganization to consolidate the House and Senate intelligence committees.

"You wouldn't consider a joint ethics committee. That's like intelligence -- they're both superspecially nonpartisan; you bend over backwards to take politics out," he said.

Durenberger was quoted in a recent interview with the Minneapolis Star and Tribune as saying that CIA Director William J. Casey is a "2 on a scale of 10." But the chairman said yesterday he would not ask for Casey's resignation.

"Nope. I told him I didn't hire him and I wasn't going to try to get him fired," Durenberger said.