Now we have a common enemy that is narco-terrorism... that's why we are asking [for] the support of the US

President Pastrana

President George W Bush has already urged Congress to lift the restrictions.

But a BBC correspondent in Washington says members of Congress have previously voiced concern about the suspected links between the drugs trade, right-wing paramilitaries and elements within the Colombian armed forces.

They fear US military aid might end up in the wrong hands.

Mr Pastrana is due to meet President Bush at the White House on Thursday.

Colombia's decades-long conflict has escalated since 20 February when Mr Pastrana's government broke off peace talks with the country's main rebel group, the FARC.

Negotiations with the second-largest insurgency, the National Liberation Army (ELN), are still under way.

US qualms

As the country suffers a wave of rebel bombings, the Colombians are trying to establish their country as another front in the war on terrorism, says the BBC's Bogota correspondent Jeremy McDermott.

Pastrana says the quest for peace failed due to rebel intransigence

President Pastrana has likened Colombia's struggle to that of the US against al-Qaeda and has pointed to a recent rash of rebel car bombings which have killed dozens of civilians in the last month to prove his point.

He wants the restrictions on $1bn of US military aid granted by former President Bill Clinton lifted, so that it can be used to contain the latest guerrilla offensive.

But the US Congress has reservations, and there is the shadow of Vietnam hanging over the American psyche.

There are fears that further commitment in Colombia could drag America into the 40-year civil conflict.