WASHINGTON (Reuter) - The CIA has been thrown on the defensive by charges that it helped flood U.S. ghettos with cocaine to finance rebels fighting Nicaragua"s Marxist government in the 1980s.

CIA Director John Deutch, under pressure from the Congressional Black Caucus and a wide range of others, has ordered an internal probe of the charges, which appeared in a three-part series last month in the San Jose Mercury News.

"Although I believe there is no substance to the allegations in the Mercury News, I do wish to dispel any lingering public doubt on the subject," Deutch wrote to the heads of the congressional intelligence oversight committees and two members of the California delegation on Sept. 4.

He said he had asked the CIA's inhouse watchdog, Inspector General Frederick Hitz, to finish within 60 days a review of "all the allegations concerning the agency published by the newspaper."

And what a set of allegations it is. Rep. Cynthia McKinney, a Georgia Democrat, lashed out Wednesday on the House floor at what she called the "Central Intoxication Agency," calling the drug allegations a "cloud of shame."

In its series titled "Dark Alliance," the Mercury News detailed a scheme that allegedly funneled tons of cocaine to black Los Angeles neighborhoods and returned millions in drug profits to a CIA-funded guerrilla army in Nicaragua.

"It is one of the most bizarre alliances in modern history: the union of a U.S.-backed army attempting to overthrow a revolutionary socialist government and the Uzi-toting "gangstas" of Compton and South-Central Los Angeles," the paper said.

The series traced the U.S. crack cocaine epidemic to two Nicaraguan drug dealers, Danilo Blandon and Norwin Meneses, who were civilian leaders of the CIA-backed FDN, the largest Nicaraguan "Contra" group fighting to overthrow the leftist Sandinista government.

Citing newly declassified material, court testimony and interviews, the paper alleged the pair had been recruited by the CIA to raise money for the Contras and turned to drug-running with at least tacit spy agency approval.

In his letter to members of Congress, Deutch said the CIA had "never had any relationship with either Blandon or Meneses." Nor, contrary to the newspaper report, had it sought to have information regarding either of them withheld at the recent trial of a convicted Los Angeles drug dealer, he said.

The internal CIA investigation under way seems unlikely to satisfy many prominent blacks and others who want an independent probe. On Saturday, the White House drug control policy director, retired Army Gen. Barry McCaffrey, joined those calling for a "full and thorough investigation."

Asked if the CIA would welcome an outside probe, spokesman Mark Mansfield declined to answer directly but said: "We will cooperate fully with any review of this matter."

An investigator who looked into Contra drug trafficking for a Senate panel in the late 1980s said he concluded that individual CIA officers in the field knew of the trafficking but the information was not passed up their chain of command.

"To say that the CIA was moving crack cocaine into California is, I think, clearly wrong," said the former Senate aide, who spoke on condition that he not be named. But he said it was "absolutely true" that cocaine traffickers of the period had sought to buy "good will" in their shadowy netherworld by funding Contra guerrillas.