Colombia is the third largest recipient of US military aid, receiving training and equipment as part of a $1.3bn anti-drug package.
He made his promise during talks in Washington with Colombian President Andres Pastrana, which focused on the battle against illegal drugs as well as trade issues.
He also said a co-ordinated effort was needed against illegal drug trafficking ''that is financing violence in my country and maybe also in part of your country.''
Military aid
Mr Bush said he understood the difficulties facing Colombia, the world's largest cocaine producer.
''We're fully aware of the narcotics that are manufactured in his country,'' he said. ''I also told him that many of the them wouldn't be manufactured if our nation didn't use them.''
Colombia is the third largest recipient of US military aid, receiving training and equipment as part of a $1.3bn anti-drug package.
Many Americans are worried about the escalating level of US involvement in Colombia, where the government has been fighting a 37-year war against leftist rebels.
Addressing those concerns, Paul Wolfowitz, Mr Bush's nominee for deputy defence secretary told Congress on Tuesday that he was wary of deeper US involvement that could lead to a Vietnam-style conflict.
Escalation fears
''It is essential to everyone concerned, including ourselves, to not find ourselves in a situation that we were in 35 years ago, where we were fighting someone else's civil war,'' he said.
After his talks with Mr Pastrana, Mr Bush repeated the US position that it would not take part in peace talks between the Colombian Government and the main leftist rebel group, FARC.
''This is an issue that the Colombian people and the Colombian president can deal with,'' he said. ''We're glad to help Colombia in any way to make the peace. We'll be glad to help the Colombian economy through trade, but I won't be present for the discussions.''
Mr Pastrana had argued that the presence of US observers would speed up the peace process which began two years ago.
Last week, FARC invited the US and Cuba to join the European Union and other Latin American countries as observers to the talks.