U.S., Colombia Pledge Mutual Drug Case Aid : Agreement: The action is intended to counter the South American nation’s expected ban on extradition.

Attempting to put the best face on the likely loss of a key weapon against Colombian drug kingpins, Atty. Gen. Dick Thornburgh said Tuesday that the United States and Colombia share the “common goal” of seizing major traffickers and bringing them to justice.

In 1989 when Colombia began extraditing Colombian drug violators to the United States, Thornburgh hailed the practice. The far more severe sentences meted out here were what the traffickers feared most, he said.

But now a Colombian assembly rewriting its constitution is considered virtually certain to ban extradition by this summer.

Partly to counter the anticipated setback, Colombian President Cesar Gaviria and Thornburgh announced agreement Tuesday on a procedure for each country to assist each other in the investigations and prosecutions of drug traffickers. Under the declaration of intent, either nation may deny assistance if it would jeopardize an ongoing investigation or pending prosecution.

Reflecting doubts of investigators and prosecutors over channeling evidence to Colombian authorities, Thornburgh said that the agreement would be implemented only on a case-by-case basis.

“We recognize that differences in our laws and procedures may mean that providing assistance in certain cases might make it impossible for us to go forward with prosecutions in the United States,” he said. “Thus, we will take all necessary steps to ensure that these prosecutions, supporting evidence and necessary witnesses are not jeopardized or compromised in any way by arrangements made under the declaration of intent.”

President Bush, emerging from a meeting with Gaviria on Tuesday, said that the United States on Monday had agreed to provide $41 million to Colombia--$20 million of it immediately--to help ease the damage that the drug war has done to government programs.

Bush said that he also told Gaviria that the United States will sign a multimillion-dollar agreement to expand long-term support to strengthen the Colombian judicial system.

Top U.S. antidrug officials concede that scrapping extradition could cripple Gaviria’s policy of persuading cartel leaders to give themselves up. But they insist that Gaviria’s efforts against traffickers have scored significant successes, particularly against second- and third-tier figures.

The White House was anxious to produce an agreement for exchanging narcotics evidence as a sign that Bush’s Andean strategy, which was drawn up just a year ago with Colombia, Peru and Bolivia, has renewed momentum.

The Gaviria-Bush meeting has importance beyond U.S.-Colombian relations. What had been the most promising of the Administration’s anti-narcotics efforts--persuading the Andean growing and producing countries to mount an all-out attack with U.S. aid on the drug interests--seems to be foundering for reasons peculiar to the politics of the countries.

“Offering drug traffickers lenient judicial treatment in exchange for their surrenders is not a bad idea per se,” said one U.S. official in Colombia familiar with narcotics matters. “We think, however, that the Gaviria administration is running the risk of giving traffickers too much in exchange for too little.”

The problem is that crimes that carry a life sentence in the United States, including murder, carry a maximum of 30 years in Colombia.

And, Pablo Escobar, a Medellin cartel leader who is accused of masterminding a terrorist campaign that killed hundreds in 1989 and 1990, could receive maximum punishment of only 15 years if he were to confess to at least one crime. That is because the maximum 30-year sentence for murder has been cut in half by Gaviria’s offer of leniency. Further reductions, codified by Colombia law for good behavior and the like, could lead to Escobar’s release in five to 10 years.

A Colombian presidential aide said in Bogota that the Gaviria administration is “worried by the possibility of light sentences for drug traffickers.”

The threat of extradition “is important to President Gaviria’s program--an important lever to get traffickers to surrender,” said Robert C. Bonner, administrator of the Drug Enforcement Administration. Without it as a means of inducing traffickers to give themselves up, “the only thing (Colombia) can do is offer unacceptably lenient sentences.”

Ostrow reported from Washington, and Yarbro reported from Bogota.