President Obama said Saturday that international forces are succeeding in their mission in Libya after a week of U.S.-led air strikes. But forces loyal to Libyan leader Muammar al-Qaddafi are still a potent threat to civilians, say Pentagon officials who are considering expanding the firepower and airborne surveillance systems in the military campaign.

Obama also readied for a speech to the nation Monday evening to explain his decision-making on Libya to a public weary of a decade of war.

"The United States should not and cannot intervene every time there's a crisis somewhere in the world," Obama said in the speech Saturday. But with Qaddafi threatening "a bloodbath that could destabilize an entire region ... it's in our national interest to act. And it's our responsibility. This is one of those times."

U.S.-led forces began missile strikes last Saturday to establish a no-fly zone and prevent Qaddafi from attacking his own people.

Obama spoke with Democratic and Republican congressional leaders about Libya on Friday afternoon. Sen. John McCain, R-Ariz., said he was concerned that the current military action might not be enough force Qaddafi from power, his spokeswoman said.

Brooke Buchanan said McCain, the top Republican in the Senate Armed Services Committee, supports the military intervention but fears it could lead to a stalemate that leaves Qaddafi's government in place.