BOGOTA -- Colombian President Andres Pastrana has failed to sever the ties between his military and right-wing militias who've massacred thousands of civilians, Amnesty International said Thursday.

The president's ''expressed will to combat paramilitary groups is not functioning and is not being respected at the local level,'' the group's chief Latin America representative, Javier Zuniga, told a news conference.

Zuniga, who was concluding a three-week fact-finding visit, said local military commanders are defying orders to reign in the rightist militias who say their victims are clandestine guerrilla collaborators. He did not name the officers, saying Amnesty would issue a full report later.

The delegation visited the northeastern state of Norte de Santander, where a rash of paramilitary killings in August prompted Pastrana to fire the regional military commander for negligence. Gen. Alberto Silva was the third general sacked for alleged paramilitary ties since Pastrana took office in August, 1998.

Zuniga called the first-ever firings of high-ranking officers for human rights abuses a ''good, first step.''

Army tolerance for the militias continues, as evidenced by the presence in one town in Norte de Santander of a paramilitary roadblock just ''100 meters (yards) away from an army roadblock,'' fellow Amnesty official Susan Lee told reporters.

In another region the group visited, militia groups and police and soldiers hold friendly soccer games against one another, she claimed.

Efforts to reach Colombia's defense ministry for comment Thursday were unsuccessful.

In a related development, the U.S-based organization Human Rights Watch this week accused the government of failing to enforce arrest warrants against two army officers who are currently on trial for the 1994 assassination of a leftist senator.

In a letter sent to Pastrana on Wednesday, the group claimed Sgt. Hernando Medina and Sgt. Justo Gil ''remain on active duty and move freely about Colombia'' flaunting the orders confining them to a military base. Prosecutors believe the two arranged the killing of communist Sen. Manuel Cepeda in concert with Carlos Castano, Colombia's top paramilitary boss.

The charges by two leading human rights organizations come as the Clinton Administration and the U.S.

Congress are considering a substantial military aid hike for Colombia beyond the nearly dlrs 300 million going this year largely to the country's anti-narcotics police.