A network of conservative activists and former military and intelligence officials, including several members of a Pentagon advisory panel on Central America, has stepped up efforts to funnel private "humanitarian" aid to Nicaraguan rebels, according to interviews with several members of the group.

Retired general John K. Singlaub, president of the World Anti-Communist League, said he and others have raised about $500,000 a month from wealthy U.S. citizens and groups since Congress cut off funds for the CIA-backed "contras" fighting Nicaragua's Sandinista government.

Singlaub said he and others have sent millions of dollars in uniforms, food, medicine and other aid to contras or their families and to refugees in Honduras, El Salvador and Guatemala.

He said the Defense Department has helped coordinate the private aid, but a Pentagon official said the military still is gearing up to help and has done little in the past few months.

Singlaub, who was recalled from his command in South Korea and then allowed to resign from active duty after he criticized President Jimmy Carter, also said that he and others have formed a private institute to train Salvadoran police forces and possibly contra soldiers if the U.S. government will not.

He said the Institute for Regional and International Studies in Boulder, Colo., has not performed any training, although it has sent survey teams to the region.

Alexander M.S. McColl, military affairs editor of Soldier of Fortune Magazine and director of the institute, was in El Salvador last weekend to meet with officials to discuss possible technical assistance programs.

Singlaub headed a panel that met at the Defense Department late last May to study the wars in Central America and offer advice on U.S. military policy.

The panel, first reported by Peter H. Stone in The Nation magazine, met at the request of Fred C. Ikle, undersecretary of defense for policy. Besides Singlaub, it included veterans of guerrilla warfare in the Philippines, Korea and South Vietnam, including retired generals Edward G. Lansdale and H.C. Aderholt.

The eight-member panel issued an eight-page classified report urging the United States to move away from conventional warfare tactics in El Salvador and apply the lessons of counterinsurgency warfare learned in Asia, including increased emphasis on psychological warfare, civic action and small-unit operations. Lansdale said the panel discussed the civil war in Nicaragua and in El Salvador, but he declined to discuss its recommendations.

"We were trying to get them to work with the people, to be the brothers and protectors of the people, instead of just going in shooting the people," Lansdale said, referring to the Salvadoran army and its U.S. advisers.

Aderholt, who heads the 1,500-member Air Commando Association in Fort Walton Beach, Fla., said that the Singlaub panel criticized the Pentagon for thinking in conventional warfare terms that will not work in El Salvador.

"The U.S. military is a firepower, high-tech outfit, and that's not what's needed," he said. "That's what our Army likes to do; they like to never see 'em, just shoot 'em."

A senior defense official said that about half of the panel's recommendations have been adopted, including an emphasis on light weapons instead of 105 mm howitzers and a move toward AC47 gunships with rapid-firing guns instead of A37 Dragonfly planes that drop 500-pound bombs. The official said, however, that a recommendation to send psychological warfare advisers to El Salvador has not been implemented.

Half of the panel members also are involved in private efforts to send aid to refugees and conservative forces in the region. They said any "nonlethal" aid to the contras or to Salvadoran refugees increases good will toward the United States and allows local armies to spend more money on arms.

"The thing that drives the commies nuts is positive action, food and medicine into those areas," F. Andy Messing Jr., director of the National Defense Council, said at a White House briefing this week.

Messing said he has brought 54 tons of food and medicine into El Salvador this year. Faith Ryan Whittlesey, assistant to President Reagan for public liaison, introduced Messing at the White House briefing by praising "the courage that Andy has displayed and the effectiveness of the program that he is administering."

But Messing criticized the administration for not providing more assistance, saying "there's a lot of bureaucratic foot-dragging going on." He said that, except for a few shipments that have been carried by the U.S. Navy or Air Force, most deliveries have been sent privately.

Aderholt agreed that the Defense Department has not helped much because of congressional opposition. He said his Air Commando Association has distributed $4.5 million in food and medicine in El Salvador provided by the Christian Broadcasting Network and World Medical Relief and is preparing similar shipments for refugees in Guatemala.

Aderholt complained that liberals in Congress "try to tie it to some sinister plan with the CIA," which he said is incorrect. But he said he would not deny that some of the aid reached the contras.

Singlaub, on the other hand, said that his U.S. Council for World Freedom has received substantial coordinating help from the Pentagon in its humanitarian efforts. He said his group, working with several others including Aderholt's, has distributed more than $6 million in food and medicine to Miskito Indians and contra families in Honduras and to refugees in El Salvador.

"We are encouraging this, because government aid has been cut off to the FDN," he said, referring to the main CIA-organized rebel front. "We became disappointed when we discovered that most aid from other organizations was going to the communists."

Singlaub said his relief effort initially was aided by persons working for Nestor D. Sanchez, deputy assistant secretary of defense for inter-American affairs.

"Nestor had in his office a few people who spent full time trying to help us coordinate our relief," Singlaub said. "Then they were centralized somewhere else."

Robert K. Wolthuis, coordinator for humanitarian assistance in the Pentagon, said the military has not provided transport for any aid in recent months. He said his office still is coordinating procedures for offering such aid, which Congress authorized in fiscal 1985, with the State Department and Agency for International Development.

Wolthuis that he hopes to have those procedures in place by month's end. He said he does not know whether aid to contra families then will meet the Defense Department's test for humanitarian assistance, which forbids aid to fighting forces, because the criteria still are being developed.

Congress authorized the Pentagon to transport humanitarian aid to Central America in what is known as the "Denton amendment" to the fiscal 1985 defense bill, named for its sponsor, Sen. Jeremiah Denton (R-Ala.). The legislation authorizes the Pentagon to use ships and planes on a space-available basis to transport food and medicine to the region, but no weapons or military equipment may be carried.