BOGOTA, Colombia (AP) _ Authorities imposed curfews Wednesday on Medellin and nine other cities in the heart of cocaine country in an effort to curb violence by drug barons stung by Colombia's crackdown on narcotics.

Also Wednesday, the U.S. government ordered families of its embassy staff to leave Colombia, a spokesman said. The order apparently was given because of fears of attacks by drug traffickers. It would apply to about 50 relatives of embassy staff, the source said on condition of anonymity.

Embassy officials also recommended that American students in Colombia leave. Last week, the State Department began urging U.S. tourists to bypass Medellin.

A shipment of weapons bound for Medellin was intercepted, and authorities said three more judges resigned in the city that reputedly supplies the United States with 80 percent of its cocaine.

More than 100 judges have resigned since drug traffickers vowed to retaliate for a crackdown on drug trafficking.

The curfews imposed Wednesday by Interior Minister Orlando Vasquez affect a total of about 3 million people. He said the mayors of the municipalities under the curfew have broader powers to conduct searches, inspect vehicles and arrest suspects.

Medellin Mayor Juan Gomez Martinez said the curfew is in effect from 10 p.m. to 6 a.m. for all vehicles and pedestrians, will remain in effect indefinitely in Colombia's second-largest city, ''until the nights in Medellin quiet down.''

The industrial city of about 2 million people, 215 miles north of Bogota, is home to the world's largest cocaine cartel. Medellin has suffered almost daily bombings by the traffickers, who are pressing the government to end its 12-day-old campaign and negotiate a peace.

In a Medellin news conference broadcast by the national radio chain Caracol, Gomez Martinez said there would be no exceptions to the curfew. ''We will not give safe conduct passes,'' he said.

Gomez Martinez complained of a lack of security assistance from the national government. He has asked for 3,000 additional national police officers to bolster the existing force of 4,000. He said the government agreed to provide an extra 100.

The mayor favors talks with the traffickers, but said at the news conference that the suggestion had been rejected by the government, and that he was carrying out all anti-narcotics measures ordered by national authorities.

Communications Minister Carlos Lemos Simonds said on Tuesday, ''There will be no dialogue.''

At midday, Mayor Escobar Perez anounced an identical curfew in the town of Itagui, 10 miles south of Medellin.

Vasquez ordered the curfew extended to eight other communities near Medellin. They are Bello, La Estrella, Envigado, Sabaneta, Rionegro, Copabacana, Guarne and Caldas.

''Medellin has become a center of perturbation in the country,'' Vasquez told reporters.

On Tuesday night, police in Medellin interrupted an attempt to rocket a state-owned distillery in Medellin.

Since the government launched its offensive and drug barons responded with a declaration of war, the city and surrounding communities have been rocked by at least 17 bombings and three arson attacks, according to police reports.

In the city of Pereira, 110 miles west of Bogota, police frustrated an attempt to kill the mayor and a city councilman, Radio Caracol reported.

Caracol said an armed suspect was arrested in the city hall, but said the motives for the attempt remain unclear. There was no immediate indication whether it was related to trafficking.

The report said Pereira Mayor Jairo Arango Gaviria and councilman Raul Velez del Corral had been the target of frequent death threats. It said security had been boosted for both men.

National police said they intercepted an arms shipment apparently bound for Medellin. A spokesman said the weapons, including 169 grenades for use with a launcher, 40 fragmentation grenades and 600 firearms cartridges were found in a truck carrying foodstuffs, which stopped on Bogota-Medellin highway at La Dorada, 75 miles north of Bogota.

The government crackdown was sparked by a 48-hour wave of assassinations, capped by the slaying of a highly popular presidential candidate, Sen. Luis Carlos Galan, on Aug. 18.

Hundreds of homes, office buildings and other properties owned by traffikers have been impounded along with cars, aircraft, yachts and other goods. The army estimates the value of the property at more than $200 million. Several midlevel trafficking suspects have been arrested.

According to local newspaper and radio reports confirmed by a judge's assistant Wednesday, three Medellin judges investigating assassinations resigned because of death threats. The reports said two of them are believed to have fled the country.

The assassinations under investigation were those of national police Col. Waldemar Franklin Quintero, Judge Maria Helena Diaz Perez and the governor of Antioquia Province, Antonio Roldan Betancur. All three killings are blamed on traffickers.

A total of 108 judges have resigned since the government's offensive began, mostly in protest over what they feel is a lack of adequate security, according to the national judicial employes' association. The Supreme Court has been rejecting the resignations and ordering the judges to resume their duties.

Since 1981, 220 judges, magistrates and judicial aides have been killed in the traffickers' highly successful campaign to cow the courts and avoid proscution.