A U.S. deficit reduction plan that promises $4 trillion in savings over time would be a good downpayment on getting the country's strained public finances under control, said John Chambers, chairman of S&P's sovereign ratings committee.

S&P has warned it may cut the United States' top AAA credit rating even if a deal on raising the government's debt ceiling is not accompanied by a credible plan to cut the deficit.

Republicans and Democrats have clashed over the role tax cuts should play and are pushing separate plans, both of which fall short of $4 trillion in savings.

Republicans have refused to raise the country's $14.3 trillion borrowing limit without a deal, and Treasury says it will run out of money to pay its obligations by August 2.

(Reporting by Walter Brandimarte and Daniel Bases; Editing by Padraic Cassidy)