FACTBOX: Presidential candidates on trade

(Reuters) - Following are the 2008 U.S. presidential candidates' positions on free trade as Canada and Mexico on Tuesday brushed aside criticism of the North American Free Trade Agreement at a summit with President George W. Bush.

DEMOCRATIC SEN. HILLARY CLINTON OF NEW YORK

* Urged renegotiating NAFTA to strengthen provisions on labor and environment. Warned of opting out from the treaty if Canada and Mexico refuse.

* Opposed free trade agreements with Colombia, Panama and South Korea but supported a pact with Peru in December.

* Pushed for increasing enforcement of U.S. trade laws, including pursuing more complaints with the World Trade Organization, using a provision that would allow outside groups to petition the government about unfair practices by trading partners and create an Intellectual Property Enforcement Network.

REPUBLICAN SEN. JOHN MCCAIN OF ARIZONA

* Supports free trade pacts with Colombia, South Korea and Panama and negotiating a new free trade pact with the 27 nations of the European Union.

* Opposes changing NAFTA agreement.

* Favors opening new trade markets, but also advocates education and retraining for workers displaced by global trade.

DEMOCRATIC SEN. BARACK OBAMA OF ILLINOIS

* Urged renegotiating the NAFTA to strengthen provisions on labor and environment. Warned of opting out from the treaty if Canada and Mexico refuse.

* Opposed free trade pacts with Colombia and South Korea but supported an agreement with Peru.

* Supports pressuring World Trade Organization to better enforce agreements and halt government subsidies to foreign exporters and imposing other nontariff barriers on U.S. exports.

* Wants to revamp fast-track trade negotiating authority to require pre-screening of potential U.S. free trade partners based on their labor and environmental standards and other factors.

(Reporting by Jeremy Pelofsky, editing by Philip Barbara)