The US Senate could start debating its final healthcare reform bill as early as Tuesday, pitting Democrat against Democrat over the controversial question of abortion coverage.

The debate puts Barack Obama, who campaigned as pro-choice, in the middle of one of the most emotional and enduring debates in US politics, potentially forcing him to take sides on an issue he has tried to avoid since becoming president.

The House of Representatives this month passed a healthcare reform bill that would sharply curtail access to abortion. Several Democrats in the Senate have said they want similar restrictions in their own bill.

Harry Reid, the Democratic leader in the upper chamber, is “still consulting with members of his caucus” on the abortion issue, one aide said, and it is not yet clear whether he will include the restrictions.

“This is a horrible dilemma,” said Larry Sabato, a political science professor at the University of Virginia. “The Democrats have to pass something – they have no choice,” he said, adding that they have backed themselves into a corner by making healthcare reform a priority.

The House passed a bill including the “Stupak-Pitts” amendment, which not only prevents abortion coverage in the public health insurance option but also prohibits private health insurers that have any customers receiving federal subsidies from offering abortion coverage to anyone else.

This is sharply more restrictive than even the 1976 Hyde amendment, which banned the use of federal funds to pay for terminations, and pro-choice activists say it amounts to a de facto ban on abortion.

“It would be a great irony if we worked so hard to elect a pro-choice president and this law passed on his watch,” said Terry O’Neill, president of the National Organisation for Women, one of the pro-choice leaders who met Rahm Emmanuel, the president’s chief of staff, this week to lobby against such measures.

“This would basically sweep aside Roe v Wade. Women are calling us and they are furious,” Ms O’Neill said, referring to the 1973 Supreme Court decision legalising first- trimester abortions.

Kirsten Gillibrand, New York senator, gathered prominent pro-choice advocates, including feminist Gloria Steinem, on Monday to protest what she called a “discriminatory and dangerous anti-choice provision”, one that would “prevent women from purchasing reproductive insurance with their own money and put the health of millions of women and young girls at grave risk”.

Mr Obama has tried to avoid talking about abortion since taking office, instead stressing the need to reduce unwanted pregnancies, but is now being drawn into the debate.

“This is a healthcare bill, not an abortion bill,” Mr Obama told ABC News last week. “We’re not looking to change what is the principle that has been in place for a very long time, which is federal dollars are not used to subsidise abortions.”

Mr Reid, who is facing a tough re-election campaign in Nevada next year, will have a difficult balancing act as Democrats occupy 60 seats in the Senate – the exact number needed to pass a bill.

Both camps are saying they have the upper hand. Barbara Boxer, a California liberal, last week said that supporters of stronger restrictions on abortion funding would not be able to muster 60 votes. “It is a much more pro-choice Senate than it has been in a long time,” she told the Huffington Post.

But Ben Nelson, a moderate from Nebraska, said he would not vote for healthcare reform unless it included the abortion provisions and a handful of other “blue dog Democrats” have signalled the same.

“I think it’s extremely likely that they can get this through the Senate, with the leadership of Ben Nelson,” said Marjorie Dannenfelser, president of the Susan B. Anthony List, a group that seeks to elect female candidates who oppose abortion.

But can Mr Obama put his signature on a bill – the Senate and House leaders plan to have one on his desk by the end of the year – that would go against the principles he has long espoused?

“He has staked so much of his future on this healthcare bill,” said Bill Galston, a former Clinton administration adviser now at the Brookings Institution. “If it comes to his desk [with a Stupak-style clause], the president is not going to veto it for that reason. He will then have to start the task of public explanations.”