Washington ? President Bush heads into his second term amid deep and growing public skepticism about the Iraq war, with a solid majority saying for the first time that the war was a mistake and most people believing Defense Secretary Donald H. Rumsfeld should lose his job, according to a new Washington Post-ABC News poll.

While a slight majority believes the Iraq war contributed to the long-term security of the United States, 70 percent of Americans believe these gains have come at an “unacceptable” cost in military casualties. This led 56 percent to conclude that, given the cost, the conflict there was “not worth fighting” — an eight-point increase from when the same question was asked last summer, and the first time a decisive majority of people has reached this conclusion.

Bush lavished praise on Rumsfeld at a morning news conference Monday, but the Pentagon chief can be glad he answers to an audience of one. Among the public, only 35 percent of respondents approved of his job performance, and 52 percent said Bush should give Rumsfeld his walking papers.

While the results were bad for Bush as people look at past decisions — whether the Iraq war should have been waged in the first place — the president has more support for his policies over the choices he faces going forward.

A strong majority, 58 percent, supports keeping American military forces in Iraq until “civil order is restored,” even in the face of continued U.S. causalities. By a slight margin, 48 percent to 44 percent, more voters agreed with Bush’s position that the United States is making “significant progress” toward establishing democracy in Iraq.

A total of 1,004 randomly selected Americans were interviewed Dec. 16 to 19. The margin of sampling error for the results is plus or minus three percentage points.