Maryland Gov. Martin O'Malley's gun-control bill has been amended more than 70 times by the General Assembly. (Aaron C. Davis/The Washington Post)

As Maryland Gov. Martin O’Malley’s gun-control bill heads to a final vote in the House of Delegates on Wednesday, all of the major provisions remain intact: His bill would ban scores of assault weapons, limit magazine capacity to 10 bullets, require fingerprinting and licensing of gun buyers, and expand the list of mental-health patients precluded from purchasing firearms.

But several key changes to the legislation are forcing advocates to make a choice during the last week of the session: Should they be happy getting most of what they want, or should they push for further measures that could risk passage of the entire bill?

Lawmakers close to the negotiations said that barring last-minute changes on the House floor Wednesday, they may have to risk sending the gun bill to a conference and, therefore, a series of high-stakes votes on the final day of the session.

One of the chief concerns is a provision that would let any state resident who volunteers to be a member of the Maryland Defense Force elude many restrictions on gun purchases. The Maryland Defense Force, which dates to 1917, is a little-known part of the state’s military department that, like the National Guard, is under the governor’s control.

Maj. Gen. James Adkins, head of the Maryland National Guard, wrote to legislative leaders Tuesday saying he opposed the exclusion. He called the force an “outstanding organization” but said many of its 450 volunteers have no military training and no need for weapons to carry out their duties. “This group of fine men and women are not a group in need of an exemption” from the gun bill, Adkins wrote.

Senate Democrats are preparing to consider several proposals that aim to limit gun violence, but a controversial ban on hundreds of weapons and parts is unlikely.

Gun-control supporters were also split on whether to risk delaying final passage to roll back a change made by the House that could allow future assault rifles to be legal.

Late Tuesday, the House advanced the governor’s bill to a final debate and vote scheduled for Wednesday. After a heavy reworking of O’Malley’s legislation last week by two House committees, the bill would ban more than 40 types of existing assault rifles, including all models of the AR-15, which was used by the alleged Aurora, Colo., shooter; the gunman in Newtown, Conn.; and the Beltway snipers.

But the House committees erased the part of O’Malley’s bill listing several physical traits used to evaluate whether weapons manufactured in the future should also be banned. That creates a loophole, critics contend, that could allow future generations of weapons to be legal that otherwise would be banned.

For example, under the current version of O’Malley’s bill, it is likely that a semiautomatic rifle under development by Beretta would be legal in Maryland. The rifle, which is expected to be called the ARX-100, is modeled after a military rifle used by Special Forces units.

Another change would allow residents to continue purchasing such assault weapons after the bill takes effect later this year. Marylanders could continue to purchase guns labeled assault weapons after Oct. 1 as long as they can show proof that the sale was initiated before the bill took effect.

The change does not specify what would constitute proof of sale prior to Oct. 1.

Vincent DeMarco, president of Marylanders to Prevent Gun Violence, said his group was urging the Senate to accept the House version despite the amendments.

“This bill accomplishes what we set out to accomplish” DeMarco said. “It really is a tremendous lifesaving measure the way it is.”

He pointed to the 10-round limit on magazines, which he said would curb the lethality of any future assault weapons.

Some advocates, however, also dislike a measure added in the House that would exempt current owners of assault weapons from having to register their guns. Under the original version of O’Malley’s bill, owners of about 60,000 semiautomatic firearms in Maryland would have been required to register their weapons before next year or face criminal penalties, including possible jail time.

Another change: Maryland would roll back its minimum age of 21 to purchase handguns for those serving in the National Guard or branches of the military.

Opponents of the measure say it is poorly worded and could allow teenagers who have never served to legally buy guns.

It had been assumed such changes would be reviewed and negotiated one last time by a conference of supportive lawmakers from both the House and Senate.

But with time in the session running out, that is no longer a certainty, key lawmakers said. The final version that passes the House could be the one O’Malley (D) would be left to sign into law.

It’s also been 17 years since Maryland passed its last major gun-control legislation. Given that, advocates may not want to wait for their next chance to get exactly the bill they want.

“It’s too early to tell. We’ll have to wait and see,” said Sen. Brian E. Frosh (D-Montgomery), who chairs the committee that will decide whether the Senate should go along with the version that emerges from the House.