WASHINGTON, Aug 2 (Reuters) - U.S. officials want to tinker with the mix of chemicals fueling missiles and rockets to gain an advantage in the Pacific by increasing the range of its front line munitions so U.S. forces can operate further away from China.

The Pentagon and Congress are looking at a retrofit that could extend ranges for some current weapons as much as 20% by using more powerful propellants and lighter warheads, two congressional aides and two U.S. officials said who spoke to Reuters under the condition of anonymity because they were not authorized to speak publicly.

Last week, the Senate revealed bill language earmarking at least $13 million to plan, expand and manufacture chemical compounds that can be used to propel missiles, or replace the explosive material in warheads, known as "energetics".

Although a fraction of the $886 billion defense bill making its way through Congress, the funding starts a process that could ultimately lead to billions of dollars of new spending on munitions.

The Democrat-controlled Senate and Republican-held House of Representatives still need to negotiate final funding levels for the concept, but there is general agreement on the bipartisan effort to deter China.

The "distance in the Indo-Pacific and sheer size of (China's) Navy means the U.S. needs more ship-killing missiles that can reach distant targets," Representative Mike Gallagher told Reuters. China views the U.S. in the Pacific as a threat, ramping up its own military presence in response.

"Unfortunately, the Pentagon has grown complacent using 1940s-era energetics and neglected advanced energetics like CL-20 that are necessary to increasing the range and lethality of our force. Every foot farther a missile can travel is a foot farther an American service member is from danger."