As the House and Senate committees on the Iran-contra affair continue their probe outside the glare of the television lights, two other congressional panels are investigating the alleged involvement of the Nicaraguan contras in narcotics trafficking.

For months, subcommittees of the Senate Foreign Relations Committee and the House Judiciary Committee have been trying to determine what fire, if any, fuels the smoky cloud of accusations that has long surrounded the contras. Among the charges is that the contras have benefited financially from the activities of drug smugglers.

In the Senate, the Foreign Relations subcommittee on terrorism, narcotics and international communications, chaired by Sen. John F. Kerry (D-Mass.), has been exploring alleged cooperation among various drug smugglers and contra elements as part of a broader probe of narcotics networks and their influence in the Western Hemisphere. Among other issues, the committee has been pursuing charges raised in an October 1986 Kerry staff report that drug traffickers were able to take advantage of the private aid network set up to support the contras.

Across the Capitol, the House Judiciary subcommittee on crime, chaired by Rep. William J. Hughes (D-N.J.), has been investigating similar reports that Miami-based fliers carried illegal weapons shipments to Central America and brought back planeloads of drugs, perhaps with the knowledge of U.S. government officials.

The House panel also is looking into allegations that Justice Department officials in Washington tried to impede a federal investigation that threatened to publicize purported gun-running out of southern Florida. Attorney General Edwin Meese III has called the charges unfounded.

Republicans and Democrats alike said they have no solid evidence that contra organizations or their current leaders have traded in drugs. Some of the contras' defenders agreed, however, that individuals within the contra movement or on its periphery were involved in drug smuggling. Moreover, they said, it appears a number of known drug traffickers participated in the contra-resupply operation.

The investigations have been complicated by a variety of problems, including less than full cooperation from federal officials, limited resources and a sometimes weak trail of documents, committee and staff members said. But members said their most difficult task may be to corroborate the testimony of some of their key witnesses -- convicted drug smugglers, whose credibility they question.

As far as the contras are concerned, "we're probably going to be able to put together a web of circumstantial material," said Jack A. Blum, special counsel to the Senate committee and one of the chief investigators in the drug probe. "I can't say to you I'm going to establish a case beyond a reasonable doubt. The case doesn't lend itself to that kind of proof."

Both committees hope to hold public hearings in late September or October.

Kerry, who publicized allegations of a contra-drug link last fall and whose own concerns initially centered on the contras, widened his focus after becoming chairman of the subcommittee earlier this year. He now considers the alleged contra connection to be only "an incidental piece of a larger picture."

At issue, along with the rebels' character and reputation, is the U.S. government's commitment to enforce the law against criminals whose activities might advance foreign policy objectives, congressional investigators said. An overarching issue, Kerry said, is how "the power of the narco-dollar" has come to affect governments and policies.

Based on State Department statements in June 1986 and documents introduced in the Iran-contra hearings, Kerry said, it is "a known fact" that some individuals connected to the contra movement were also involved in narcotics. The unanswered question, he said, "is what was the nature of it, and the extent."

The committee met behind closed doors Thursday with former Central Intelligence Agency operative Felix Rodriguez, also known as Max Gomez. An earlier witness, Ramon Milian-Rodriguez, reportedly alleged he funneled nearly $10 million from a Columbian cocaine cartel through Rodriguez to the contras. Milian-Rodriguez said the cartel believed it was currying favor with the U.S. government, according to sources familiar with his testimony.

Investigators for Sen. Jesse Helms (R-N.C.), who has worked closely with Kerry on the probe, said both senators are determined to follow the narcotics trail wherever it leads. They said they do not expect the committee's findings to damage the contras' cause, even if they do implicate individuals who had associations with the contras.

Kerry declined to discuss his findings in detail, and the House investigation has been proceeding with similar caution. The crime subcommittee chairman said he has deliberately kept his investigation out of public view and has kept all the information it has gathered confidential to prevent "wild allegations" from ruining reputations.

"We just don't know what we have. There seems to be some substance to some of the charges, and there appears to be little substance to other charges that have been made," Hughes said. "We haven't established anything."

Among the more sensitive charges is that U.S. officials, including CIA agents, "winked and looked the other way" while illegal activities occurred, members said. The CIA denies such allegations.

The crime subcommittee has responsibility for overseeing enforcement of narcotics, firearms and money-laundering laws. It began its inquiry about nine months ago after new stories surfaced suggesting that contras were receiving drug-trafficking profits.

Members of the committee staff have traveled to Central America to track down information, and an investigator hired by the panel has been doing research in Miami. The staff has interviewed about 30 witnesses, Hughes said.

In addition, it recently received material collected by the House Select Committee on Narcotics Abuse and Control, which is letting Hughes take the lead in the investigation. The chairman of the narcotics panel, Rep. Charles B. Rangel (D-N.Y.), said people in the contra movement were apparently connected to the narcotics trade, but he added that the committee received no proof that the contra leadership has supported its operations through drug trafficking.

The crime subcommittee recently cleared a major hurdle when it privately questioned three assistant U.S. attorneys from Miami about the investigation that was allegedly thwarted by higher-ups at the Justice Department. Two spoke to the subcommittee's lawyers voluntarily after having received subpoenas; the third testified under subpoena at a closed session July 30. The three also have given depositions to the Iran-contra committees.

The investigation has divided the House panel along party lines. Some Republican members have argued that there are no grounds for the inquiry to proceed, and others have urged that the panel defer to the Iran-contra select committees.

"I really haven't seen anything that would make it worthwhile for the committee to spend any more time or money on this investigation," said Rep. E. Clay Shaw (R-Fla.). The crime subcommittee is covering territory already explored by the Iran-contra committees and is ill-equipped to conduct a thorough investigation of its own, Shaw said.

The subcommittee's ranking minority member, Rep. Bill McCollum (Fla.), who also serves on the House select committee, unsuccessfully petitioned select committee Chairman Lee H. Hamilton (D-Ind.) to declare the Justice Department case beyond the Hughes panel's jurisdiction, but McCollum did say it would be appropriate for the subcommittee to pursue the charges of gun-running and drug trafficking.