WASHINGTON (AP) — In an election-year challenge to President Barack Obama, House Republicans are pressing ahead with a defense budget that adds billions of dollars, boosts nuclear weapons programs and slows cost-cutting reductions in the force as the military emerges from two long wars.

Republicans argue that the Democratic president is shortchanging the military and leaving the nation vulnerable, requiring billions more for defense. In a reversal earlier this year, the GOP abandoned the spending levels for defense and domestic programs set last summer in the deficit-cutting agreement between Obama and Congress. They want to boost defense spending by $8 billion and offset the increase with deep cuts in safety-net programs for the poor such as Medicaid and food stamps.

The budget "helps ensure the Pentagon's new national security defense strategy is not a hollow one. And, despite historic cuts to our wartime military, it plugs critical capability and strategic shortfalls opened in the president's budget submission," Rep. Howard "Buck" McKeon, R-Calif., chairman of the House Armed Services Committee, said Wednesday at the start of three days of debate. Final passage is expected on Friday.

The GOP political argument that Obama is soft on defense has less resonance with voters after the killing of Osama bin Laden, repeated drone strikes in the war on terror and a weakened al-Qaida. Opinion surveys show that Americans give the president high marks on national security.

The overall defense bill totals $642 billion for the fiscal year beginning Oct. 1 — a base defense budget of $554 billion, including nuclear weapons spending, plus $88 billion for the war in Afghanistan and counterterrorism efforts. Obama had proposed $551 billion, plus $88 billion.

The White House has threatened to veto the measure, offering a laundry list of objections. Defense Secretary Leon Panetta slammed the House Armed Services Committee last week for restoring favorite programs, arguing that the move would mean cuts in training or equipment that could affect readiness.

Stepping up the criticism, Gen. Ray Odierno, the Army chief of staff, said Wednesday that the bill's limits on the pace of force cuts would create budget problems. The Army plans to shrink the force from a peak of 570,000 to 490,000 by 2017. The bill slows the reduction in the force, saying the Army can only cut to 552,000 by the end of 2013.

"This might cause us to force more people out of the Army than we want, instead of using natural attrition over the five- or six-year period that we've identified over the last two budget submissions," said Odierno, who added that he had spoken to House members about changing the bill.

Obama and military leaders have said their proposed spending blueprint for next year reflects a new strategy that shifts the Pentagon's focus from the Iraq and Afghanistan wars to future challenges in Asia, the Mideast and in cyberspace.

Yet, Republicans on the House Armed Services Committee crafted a bill that departs drastically from Obama's blueprint.

The legislation would require construction of a missile defense site on the East Coast, restrict the president's ability to implement a nuclear weapons-reduction treaty with Russia and spends millions more on nuclear weapons programs. The bill rejects the administration's call for another round of domestic military base closings. It snubs the Pentagon's appeal to raise the annual health care enrollment fees for working-age military retirees based on their gross pay, with hikes ranging from $35 to $140.

The bill preserves ships, aircraft and a version of the Air Force's Global Hawk drone that were slated for retirement.

The House is expected to tackle a long list of amendments on Thursday, with fights looming over accelerating the withdrawal of U.S. forces from Afghanistan and the indefinite detention of terrorist suspects, including those captured in the United States.

An unusual coalition of Democrats, libertarians and tea partyers is pushing an amendment that would bar indefinite detention without charge or trial of suspected terrorists and roll back the military custody requirement. Last year, Congress passed and Obama reluctantly signed the defense bill that included the provision allowing indefinite detention.

The president does not need this authority to keep us safe," Rep. Adam Smith of Washington state, the top Democrat on the House Armed Services Committee, told reporters at a Capitol Hill news conference.

On the eve of the debate, a federal judge in New York on Wednesday struck down as unconstitutional the portion of the law that gives the government broad powers to regulate the detention, interrogation and prosecution of suspected terrorists.

The administration also strongly objected to Republican-backed provisions in the bill that bar same-sex marriages on military installations, measures added by committee conservatives still angry with the decision to allow gays to serve openly in the military. The administration said the provision would "inhibit the ability of same-sex couples to marry or enter a recognized relationship under state law."