A convicted drug money launderer told a Senate panel yesterday he channeled illicit narcotics funds to the U.S.-backed contras fighting Nicaragua's Sandinista government after he received a request for help from "a liaison with . . . U.S. intelligence."

Ramon Milian-Rodriguez, who is serving a 43-year federal prison sentence, made the allegation while testifying that he also paid millions of dollars in bribes to Panamanian strongman Gen. Manuel Antonio Noriega.

Milian's credibility was challenged yesterday by the U.S. Attorney's Office in Miami, which prosecuted him, and the Drug Enforcement Administration (DEA).

"We have told the Senate that we just felt he was not credible," said U.S. Attorney Leon Kellner, who added that the DEA and other federal law enforcement agencies held the same opinion.

"We do not think {Milian} is a particularly credible person," a DEA spokesman said.

Kellner said his office did not call Milian as a witness in an investigation that led to the indictment last week of Noriega on drug and racketeering charges.

However, Sen. John F. Kerry (D-Mass.), chairman of the Senate Foreign Relations subcommittee that heard Milian's testimony, and Sen. Alfonse M. D'Amato (R-N.Y.) both criticized federal law enforcement officials for their opinion of Milian.

"It's rather incredible that there has not been an effort by law enforcement officials to attempt to utilize you," D'Amato told Milian after listening to his testimony.

In an impromptu news conference after the hearing, Kerry acknowledged that he was aware of the Miami prosecutors' reservations about Milian but said he has "very little respect for that particular office."

Aides to Kerry, an opponent of the Reagan administration's contra program, and other congressional officials have criticized Kellner's office in the past for what they said was his failure to pursue separate allegations of illegal gun-running to the contras.

Jack A. Blum, special counsel to Kerry, said DEA's criticism of Milian could be expected because DEA was singled out this week for not aggressively investigating past drug allegations involving Noriega. Blum noted that the subcommittee released letters showing that DEA chief John C. Lawn and his two predecessors had praised Noriega for his help in drug probes.

Blum said he closely studied the criminal investigative files on Milian and "I would not have gone near this guy unless I had substantial reason to believe in the truth of what he said."

Kerry, whose staff has been investigating for almost two years allegations of contra ties, said his subcommittee on terrorism, narcotics and international communications will focus on the contra drug allegations in new round of hearings next month.

The panel finished four days of hearings this week that centered on Noriega, Panama's military commander and de facto ruler.

Federal law enforcement officials and Kerry's staff agree that Milian, a former Miami accountant, was a major launderer of drug profits.

Milian was arrested in May 1983 after federal agents stopped a Learjet bound for Panama with him aboard and found $5.4 million in it. Records seized from Milian showed that during one eight-month period he had shipped nearly $150 million in drug profits to Panamanian banks.

Milian, a Cuban American, testified that a Cuban-American friend involved in CIA-directed operations against the government of Cuban leader Fidel Castro first showed Milian how to hide the origins and flow of illicit cash.

Milian said he employed the same techniques when he became a money launderer for drug smugglers. He said he was hired in 1979 by the leaders of the notorious Medellin Colombian drug cartel, a ring investigators say is responsible for most of the cocaine shipped into the United States.

Milian said that after his hiring, he met with Noriega, then head of Panama's military intelligence, and agreed to provide Noriega a percentage of drug profits laundered through Panamanian banks.

Sometime after his 1983 arrest on money laundering charges, Milian testified, he was asked to provide funds to the Nicaraguan contras by an individual he identified only as a "liaison" with U.S. intelligence. "Let's call him whoever was running the {contra} resupply," Milian said. Kerry directed Milian not to name the person yesterday.

In news interviews last year, Milian said his prime contact on the contra funds was Felix I. Rodriguez, also known as "Max Gomez," a former CIA agent and a key figure in a secret contra air resupply operation.

Rodriguez has strongly denied Milian's allegation.

Milian testified yesterday that some drug funds were laundered to the contras through two companies he set up. Kerry's staff has previously noted that about $230,000 in nonlethal U.S. contra aid funds passed through a bank account in the name of Frigorificos de Puntarenas, one of the companies cited yesterday by Milian.

Prosecutor Kellner said Milian never told his staff of these allegations of drug funds to the contras. At his trial, Kellner said, Milian testified falsely about the ownership of cocaine found in Milian's office.

Kellner said his office also has no "documentary evidence" that Milian was a money launderer for the Medellin drug cartel. Kellner said Milian claimed to have information on the cartel only after Miami prosecutors obtained a much-publicized indictment of top cartel leaders.

"He made a confession when he was first arrested . . . and he said he was money-laundering for major drug traffickers but he never said the cartel," Kellner said.