BY JUAN O. TAMAYO

 BOGOTA, Colombia -- A huge shipment of cocaine seized by Colombian police
 on its way to Cuba has turned into a nightmare for authorities here, sparking four
 murders and tensions between U.S. and Colombian prosecutors.

 Gunmen have killed two potential witnesses, plus the wife and son of one of them,
 and have forced authorities to transfer the 1998 case to a ``faceless prosecutor
 whose identity is kept secret to protect his life.

 One suspect's fight against his extradition from the United States is raising
 concerns that Bogota will balk at sending Colombians to face U.S. justice if
 American courts rule in his favor.

 Washington has long insisted on extraditing drug lords to remove them from a
 Colombian judicial system where they can bribe or threaten their way into lighter
 sentences and easy prison conditions.

 In a further twist to the case, the man fighting his extradition from the United
 States is the son of a Colombian senator assassinated for helping to draft the
 U.S.-Colombian treaty that allows extraditions.

 The 7.2-ton shipment in the case, one of the largest ever confiscated in Colombia,
 was found in false compartments of six freight containers seized Dec. 3, 1998, in
 the Caribbean port of Cartagena.

 The containers were loaded with barrels of plastic resin consigned to a firm in
 Havana that manufactured plastic figurines for export to Europe. The firm's owners
 were two Spaniards and a Cuban government enterprise.

 A fierce battle erupted in Washington last year as congressional conservatives
 argued that the seizure showed that Cuba should be added to the U.S. list of
 ``major transit points for U.S.-bound narcotics.

 Administration officials said there was no hard evidence the shipment was
 destined for the U.S. market, however, and President Clinton left Cuba out of the
 ``majors list he issued in November.

 Colombian counternarcotics officials and prosecutors say they believe the two
 Spaniards planned to redirect the containers from Havana to Spain, along with
 shipments of their figurines, and sell the cocaine in Europe.

 But they admit their information on the final destination of the drugs came from
 Cuba.

 ``We reached a dead end when the Cuban authorities all but guaranteed that the
 trail led only to the two Spaniards, one counternarcotics official said.

 Prosecutors say they have made progress in investigating the Colombian end of
 the shipment, valued at $23 million at Bogota wholesale prices and many times
 that at European or U.S. street sale prices.

 DENIAL OF GUILT

 Arrest warrants have been issued for the Spaniards, Jose Royo Llorca and Jose
 Herrera Campos, who deny any knowledge of the drugs. But neither Cuba nor
 Colombia has sought their extradition, and they remain free in Spain.

 Two men charged with minor roles in the shipment will soon go on trial, seven
 others are in jail while under investigation and four others are wanted for
 questioning, prosecutors say.

 WITNESS SLAIN

 The case began taking turns for the worse when a potential witness to the
 financial dealings behind the shipment, Heriberto Bengoechea, was shot to death
 in December in the city of Cali.

 Three weeks later, gunmen killed Ricardo Estrada Vergara, a suspected principal
 in the deal and owner of E.I. Caribe, the firm that was shipping the plastic resins
 to Cuba. His wife and son were shot to death in their Cali home the next day.

 Prosecutors say Estrada Vergara, a Seventh-Day Adventist, had been hiding in
 church buildings since the drug shipment was seized and may have been thinking
 about cooperating with police before his death.

 The attorney general's office transferred the case in January to one of its
 ``faceless prosecutors, anonymous officials used in cases where drug traffickers
 or criminals have threatened witnesses or court officials.

 PENNSYLVANIA ARREST

 The case took another strange turn after prosecutors issued an arrest warrant in
 December for Victor Tafur, 36, son of Sen. Donald Tafur, shot dead in 1992 for his
 work on the U.S.-Colombian extradition pact.

 Victor Tafur was arrested by FBI agents March 4 near his mother's home in New
 Hope, Pa., where he had moved to recover from injuries he suffered in the crash of
 a small plane outside Bogota early last year.

 Prosecutors say several large personal checks signed by Tafur were deposited in
 a bank account of Estrada Vergara's firm. That shows that he helped finance the
 cocaine shipment, they say.

 Tafur denies any wrongdoing and says the money came from his father's pension,
 560 million pesos, paid to his mother in 1998. He said the family wanted to
 change the pesos into U.S. dollars and deposit them in a Swiss bank.