President Barack Obama's plan to send 100 military troops to Uganda risks miring the United States in another protracted war, a top Republican lawmaker warned on Sunday.

Senator John McCain said that with almost 100,000 US troops in Afghanistan and the drawdown from Iraq still not complete, Obama's plan to send troops to act as military advisers for Ugandan government forces fighting the rebel-led Lord's Resistance Army was ill-advised.

"I worry (that) with the best of intentions we'll somehow get engaged in a commitment that we can't get out of. That's happened before in our history," he told CNN television.

McCain, an American hero of the Vietnam war, agreed that the Lord's Resistance Army has been "guilty of unspeakable behavior and the human rights organizations all over the world want this to stop."

But the high-ranking senator, the 2008 Republican presidential candidate and a leading voice in Congress on military matters, demanded an "explanation" as to why lawmakers' input was not sought before US forces were committed.

"I'm very disappointed... that the administration has not consulted with members of Congress before taking such action," McCain told CNN.

"I've been under four presidents, and this is the least communicative with Congress of any administration that I've ever seen," he said. "Maybe it has something to do with the polarization of politics, but it is unfortunate."

Obama on Friday announced that the US force would act as advisers to partner Ugandan forces trying to remove from the battlefield Joseph Kony and other senior leaders of the LRA, which has been accused of gross human rights abuses. He said the American troops would not lead the fighting themselves.

The mostly special ops units are to deploy in Uganda, South Sudan, the Central African Republic and Democratic Republic of the Congo, subject to approval of regional governments, Obama said in a message to Congress.

LRA rebels are accused of terrorizing, murdering, raping and kidnapping thousands of people in the four nations, and tens of thousands of people died in their 20-year war with security forces in northern Uganda.