Rice and the legislators met Colombian union leaders opposed the deal to hear complaints that Alvaro Uribe, the president, has failed to end violence, including murder, against their members.
"There's not a country in the world where the list of martyrs is as long as it is in Colombia," said Carlos Gutierrez, head of the CUT labour organisation, which represents Colombia's 530,000 unionised workers.
More than 700 trade unionists have been killed in Colombia since 2001, according to the government.
The number murdered annually has fallen sharply since Uribe took office in 2002, but the 25 killed in 2007 was still more than in any other country in the world.
Despite the administration's push, the AFL-CIO - the largest US labour organisation and a key Democratic party supporter, strongly opposes the free-trade deal.
Democratic presidential candidates Hillary Clinton, Barack Obama and John Edwards all oppose the deal, citing concerns over violence against trade unions.
Rice said the US congress should recognise the progress made by Uribe in demobilising paramilitary forces responsible for most of the past abuses.
"It's very obvious that just a few years ago, I think you could have said that Colombia was in danger of being a failed state, and it's come back from that," she said.
Rice also said that failing to pass the trade deal would damage the US's image in Latin America, where there is opposition to the pro-market reforms favored by Washington.
Colombia has disarmed over 30,000 right-wing paramilitaries who once fought the country's rebels and were accused of some of the worst atrocities that took place during the country's long civil war.
Nearly 70 other US congressmen have travelled to Colombia on similar visits since last summer, led by high-ranking Bush administration officials including Carlos Gutierrez, the commerce secretary.
On Friday, the delegation will meet unions that support the trade deal and a flower farm that stands to benefit from permanent duty-free access to the US market.
They will also meet with Uribe before returning to Washington.