By Valerie Volcovici

WASHINGTON, March 17 (Reuters) - The U.S. Environmental Protection Agency said on Friday it had awarded $100 million to upgrade Flint, Michigan's drinking water infrastructure to address a crisis that exposed thousands of children to lead poisoning.

The grant to the Michigan Department of Environmental Quality will enable the city to "accelerate and expand" its work to replace lead pipes and make other improvements, according to the EPA. Estimates of the upgrade's cost range from $200 million to $400 million.

Friday's announcement made the disbursement official. Last year, Congress passed and former president Barack Obama signed the Water Infrastructure Improvements for the Nation Act to allocate $100 million to aid Flint.

The EPA´s state revolving funds, which Congress can allocate to help with cleanup efforts, were one of the few programs that the Trump administration did not slash in its proposed budget for the agency.

"EPA will especially focus on helping Michigan improve Flint´s water infrastructure as part of our larger goal of improving America´s water infrastructure," said a statement from agency Administrator Scott Pruitt.

The EPA will make $31.5 million immediately available for lead pipe replacements and upgrades, and Michigan will provide a $20 million required match.

The remaining $68.5 million will come after the city and Michigan complete additional public comment and technical reviews.

"Today we have good news for families in Flint who have already waited far too long for their water system to be fixed," said a statement from U.S. Senators Debbie Stabenow and Gary Peters, and Congressman Dan Kildee, all Michigan Democrats.

Flint Mayor Karen Weaver, also a Democrat, said the funds would help the city reach its goal of replacing 6,000 pipes this year. She met briefly with President Donald Trump on Wednesday.

In January, 1,700 Flint residents filed a lawsuit in the U.S. District Court in Michigan, saying the EPA failed to warn them of the dangers of the toxic water or take steps to ensure that state and local authorities were addressing the crisis. The plaintiffs seek $722 million in damages.

Midwestern politicians are worried about the elimination in the proposed U.S. budget of funding for an effort to clean up the Great Lakes, from which some states draw their drinking water.

Flint was under the control of a state-appointed emergency manager when it switched its water source to the Flint River from Lake Huron in April 2014. The more corrosive river water caused lead to leach from pipes and into the drinking water.

The city returned to its original water source in October 2015. (Reporting by Valerie Volcovici; Additional reporting by Timothy Gardner; Editing by Lisa Von Ahn)