Sen. John McCain’s (R-Ariz.) defense policy bill is being debated in the Senate this week. (Photo by Pete Marovich/Getty Images)

The Senate is set to begin fighting on Wednesday over a defense policy bill that has morphed into a platform for contentious social issues that deeply divide Republicans.

The House has already passed its own version of the measure, which authorizes programs and spending levels for the nation’s defense programs and military campaigns. House and Senate Republicans are quibbling over the appropriate level of war funding, with different plans to try to bust budget caps agreed to in a bipartisan deal last year.

But the bigger battles are being waged over social issues, such as whether to require young women to register for the draft and whether to roll back President Obama’s executive order prohibiting federal contractors from discriminating against LGBT employees. Many conservatives feel strongly on both counts, and are unlikely to relent in an election year.

The fights could delay passage of the Senate defense bill until June. But even then, many of the more contentious issues may not be resolved until the House and Senate meet in conference to hash out their differences.

Senate Armed Services Committee Chairman John McCain (R-Ariz.) charged Minority Leader Harry Reid (D-Nev.) on Tuesday with trying to “stall” the defense bill “for pure partisan reasons,” by insisting the bill clear certain procedural hurdles. The bill cleared the first such hurdle on Wednesday morning with full support of senators in a 98-0 vote.

“It’s shameful,” McCain told reporters on Tuesday. “It’s disgraceful.”

Reid retorted on Tuesday by accusing Republicans of trying to jam a 1,664-page bill “decided in secret” and filled with “all kinds of earmarks” down the Senate’s throat without giving leaders a chance to read it.

The spat is just a preview of the political tensions around the defense spending bill, which has inflamed partisan tensions on both sides of the Capitol.

Many Republicans  — including Senate Minority Leader Mitch McConnell (R-Ky.) — have tentatively supported requiring women to register for the draft, while others vehemently oppose the idea. And the Senate bill steers clear of a House-led effort to make religious organizations holding federal contracts exempt from portions of civil rights law that would require them not to discriminate against LGBT employees, as required by a recent Obama executive order.

McCain’s bill, drafted over a series of closed-door committee sessions and released to the public on Friday, is far more conciliatory to Democrats than the House bill.

While the House bill seeks to commit an extra $18 billion in war funds to pay for Defense Department programs, McCain’s legislation sticks to last year’s bipartisan budget blueprint, avoiding the need for an emergency supplemental next spring.

But those subjects and more may be raised as debate begins.

Senators are bracing for a conservative attack on the part of the bill requiring young women to register with the Selective Service. The measure split Republicans on the Senate Armed Services Committee and is likely to do the same on the floor.

Sen. Mike Lee (R-Utah) led the challenge against the draft idea in committee and could try to do so again on the floor. Sen. Ted Cruz (R-Texas) has said that he “will continue my efforts to speak out against the effort to force America’s daughters into combat.”

The move to require women to register for the draft had an unlikely origin, when Rep. Duncan Hunter (R-Calif.) — who opposes the Obama administration’s recent decision to open up all combat roles to women — proposed the change in the House Armed Services Committee to start a “discussion.” But to GOP leaders’ surprise, the committee approved his language, prompting them to yank out the provision in a Rules Committee maneuver before it could go to the floor.

Over in the Senate, however, leaders embraced the House’s move when two-thirds of Armed Services panel members supported the idea.

The GOP divide on the issue will make it difficult for senators opposed to women in the draft to reverse the issue in the upper chamber, so the battle may have to be hashed out in conference.

As for money, McCain promised an amendment to add $17 billion to overall defense spending levels. But Tuesday afternoon, he told reporters he was undecided about whether to add that money to the Pentagon’s bottom line, or pump it into the Defense Department’s war fund – a mechanism Republicans have used to help get around budget caps.

Either way, the move is expected to face a challenge from Democrats, who object to raising defense spending without raising spending on domestic programs.

Meanwhile, a bipartisan group of senators led by New York Democrat Kristen Gillibrand and Iowa Republican Chuck Grassley are planning to revive a measure as an amendment to the defense bill to change how sexual assaults in the military are prosecuted. The measure, which would put the decision to pursue charges in the hands of a military prosecutor instead of a military commander, failed to pass on a similar vote last year, but supporters argue that new information could change some minds.

“The Senate held its previous votes under the influence of false and misleading information,” Gillibrand said, charging that Pentagon officials had misled members of Congress in testimony. “Congress must give the members of our military a justice system worth of their service.”