Bush asking him to step up American efforts to help resolve the ethnic conflict in Sri Lanka.
"The United States has the opportunity to serve as a leader" in renewed international efforts to bring about a peaceful resolution to the conflict, the lawmakers said in the letter, a copy of which was obtained by AFP.
Led by two Democrats in the House of Representatives, David Price and Rush Holt, the lawmakers told Bush it was "imperative" for him to step up US diplomatic engagement and high-level political contact in Sri Lanka in a bid to achieving peace.
Peace talks between the Sri Lankan government and Tamil Tiger rebels fighting for a separate homeland in the areas of northern and eastern Sri Lanka collapsed in October last year, leading to a sharp escalation of fighting.
Peacebroker Norway held a meeting of Sri Lanka's top aid donors last week in a bid to halt the new wave of bloodshed, but there was no breakthrough following that gathering.
More than 5,000 people have been killed in the new wave of fighting since December 2005 despite a truce in place since February 2002.