BY GLENN GARVIN

 Costa Rican authorities, alarmed by indications that their country has become a
 conduit for clandestine arms shipments headed for Marxist guerrillas in Colombia,
 announced plans Thursday for a series of checkpoints along the Pan American
 Highway aimed at staunching the flow of guns.

 The Costa Ricans also said they will press for a regional crackdown on the arms
 trade, broadening coastal patrols with the U.S. Coast Guard and seeking
 meetings with law enforcement officials in Nicaragua and Panama.

 ``This is not a problem exclusively of Costa Ricans, but regional, that has to do
 with Nicaragua, El Salvador, Honduras and Panama,'' said Rogelio Ramos, Costa
 Rica's public security minister. ``And despite the fact that it's not a new problem,
 we definitely have to confront it together.''

 The announcement came less than a week after Panamanian police seized a
 large shipment of weapons and explosives from Costa Rica that, they said, was
 destined for the Revolutionary Armed Forces of Colombia.

 The shipment -- which contained hundreds of rifles, machine guns, grenade
 launchers and land mines, as well as more than 2,000 pounds of explosives and
 73,000 rounds of ammunition -- was the third this year intercepted by
 Panamanian police on its way from Costa Rica to Colombia.

 ``It's a continuing problem,'' a Panamanian security official said. ``We don't worry
 so much about Costa Rica being a source of the weapons, but it is certainly a
 transit route from Nicaragua and El Salvador.''

 Both Nicaragua and El Salvador are awash in weapons left over from the civil wars
 that ended in both countries during the last decade. Intelligence officials up and
 down the Central American isthmus say there is evidence that not only disarming
 guerrilla groups but the downsizing armies in both nations have sold some of their
 excess weapons to Colombian guerrillas, sometimes in barter deals for cocaine.

 Colombian police, however, add that some of the weapons being supplied to the
 FARC and the National Liberation Army, a rival Marxist group, come from Costa
 Rica itself, fallout from the country's use as a launching pad for a guerrilla
 insurgency in Nicaragua more than two decades ago.

 During 1978 and 1979, more than 60 flights carrying arms for the Nicaraguan
 guerrillas -- from their allies in the governments of Venezuela, Panama and Cuba
 -- landed in Costa Rica.

 A subsequent investigation by a Costa Rican congressional committee
 discovered that a huge amount of the weapons were given to Costa Rican
 officials, including then-security minister Johnny Echeverría, as payoffs for
 permitting the arms trade. What happened to the weapons was never determined,
 but Colombian police say that some of them are turning up in guerrilla hands now.

 Regardless of where the weapons originate, there's no question that some of
 them are staying in Costa Rica for use by criminals, said Lineth Saborío, head of
 the country's national investigative police.

 Several high-profile crimes in Costa Rica this year, including a kidnapping, a
 murder and the robbery of a suburban San Jose liquor store, were committed with
 military weapons including AK-47 assault rifles and RPG-7 grenade launchers,
 she said.

 Foreign officials believe it is the involvement of military weapons in local crime as
 much as anything that prompted the measures announced Thursday by Costa
 Rican officials.

 Besides a new system of roving checkpoints on the Pan American Highway,
 which travels the length of Central America and peters out near the Colombian
 border in Panama, Costa Rica police will also set up a new unit targeted
 specifically at arms trafficking.

 Costa Rica will also seek to expand joint patrols with the U.S. Coast Guard. The
 patrols are aimed at drug merchants who use Costa Rican coastal waters, but the
 similarity in routes used by traffickers in weapons and in narcotics makes them a
 logical deterrent, Costa Rican authorities said.

 Panamanian and Costa Rican news media have reported that the police were
 tipped to the weapons shipment seized in Panama last week by the DEA.

 Herald staff writer Juan O. Tamayo in Bogotá contributed to this report.