U.S. President George W. Bush on Saturday rejected calls for a withdrawal of U.S. troops from Iraq and tried to counter growing impatience with the war by calling it a "vital test" for American security. "The mission isn't easy, and it will not be accomplished overnight," Bush said in his weekly radio address. Bush described the conflict as part of the broader U.S. war on terrorism. He said stabilizing Iraq and quelling the insurgency were important for American interests. "Some may disagree with my decision to remove Saddam Hussein from power, but all of us can agree that the world's terrorists have now made Iraq a central front in the war on terror," Bush said. "By making their stand in Iraq, the terrorists have made Iraq a vital test for the future security of our country and the free world," he added. Bush's radio address zeroed in on Iraq and the economy, two issues he plans emphasize in coming weeks. On the economy, Bush said his tax-cutting policies had put the United States "on the track to growth." He talked of his Social Security effort in the address, but put first his drive for ratification of the U.S.-Central American Free Trade Agreement and the push to rewrite U.S. energy policy.