CHAPARE, Bolivia (AP) _ Drug traffickers trying to fly out more than 400 pounds of cocaine were forced down and fled into the jungle.

Bolivia's war on drugs has become airborne, particularly since the arrival of two American AWACs radar planes that monitor air traffic in the Chapare, Beni and Santa Cruz regions, source of one-third of the world's cocaine.

Because of successes against the drug trade in Bolivia, the country's main trafficking networks have been taken over by Colombians and the result has been increasing violence, say officials of the U.S. Drug Enforcement Administration.

A year ago, few armed traffickers were in the Chapare, a tropical region the size of Delaware and New Jersey. Now, Bolivian anti-drug police and DEA agents report frequent encounters.

Hundreds of police and military personnel have conducted extensive operations in the Chapare this year, with the support of U.S. Border Patrol and DEA agents.

''Now that the principal traffickers are in jail, our focus is to disrupt the trafficking networks,'' said Carlos Saavedra Bruno, the interior minister.

Eight of the leading suspects surrendered under a government amnesty in September and October 1991 after a raid on Santa Ana, a town where the traffic was centered.

''After Santa Ana, the old Bolivian networks withered on the vine,'' said Don Ferrarone, DEA chief in Bolivia. ''Now the Colombians dominate operations, supply aircraft and are financing the major networks active in Bolivia.''

''This is going to escalate and get dirty,'' he said. ''The Colombian response is, if it's in their way, then take it out. This is business for them.

''If the money and political will holds up, this operation is designed to destroy cocaine trafficking in the Chapare.''

The drug traffic puts $300 million to $500 million a year into the Bolivian economy, compared to annual legal exports valued at $1 billion.

Checkpoints have been set up on roads leading into the Chapare. Dogs trained to sniff out chemicals and drugs accompany police and U.S. Border Patrol agents. Patrol boats scout the rivers traffickers use to ferry drugs to airstrips and to processing labs in the northern Beni region.

Traffickers are searching for alternate routes because of the AWACs planes, but ''the air program is only part of it,'' said George Auflick, head of DEA operations in the Chapare. ''We want to affect every aspect of the trafficking networks, while staying away from farmers.''

Auflick said the traffickers might be quiet for a time, as they have in the past, then resume operations over new routes.

Because of the increased operations, including raids on cocaine labs in the Beni and Santa Cruz regions, more of the coca leaf grown in the Chapare is being processed into cocaine on the spot.

Police confiscated more than 1,300 pounds of cocaine base in the Chapare during a two-week operation in April, including the load on the plane that was forced down.

Anti-drug officials say that indicates a shift in processing operations toward the Chapare, where 300,000 farmers grow coca for a living. In all of 1991, police confiscated 6,600 pounds of cocaine, about 2 percent of the estimated annual production in Bolivia.

While Bolivia appears to be making headway, law enforcement officials doubt the effort will have much effect on the general cocaine supply if Colombia and Peru continue producing it and the demand remains high.

''I think there needs to be a similar effort in Peru,'' Ferrarone said. ''There is certainly enough capacity in Peru to satisfy the world market. If Bolivia shuts down trafficking, it will put more pressure on Colombians to move into Peru. The war on drugs has to be viewed in its totality.''

''Unless we get a serious reduction in Americans using cocaine,'' he added, ''there is alway going to be an engine fueled by cash from the United States to keep this industry afloat.''