Debate was expected to be lengthy Thursday as both sides delved into such murky issues as the beginning of life and the ethics of science.
The bill would ban all human cloning - for reproduction or research - and impose a $1 million fine and 10-year prison sentence for violators. The measure passed the House 265-162 during the last legislative session but stalled in the Senate.
Supporters of research say cloned embryos hold the potential for cures to scores of diseases. Those who want to ban such research say that a cloned embryo is a human even before implantation in a womb, and to destroy it for research would be immoral.
"The issues in human cloning remain the same," said Rep. Dave Weldon, R-Fla., one of the sponsors of the bill. "If we allow embryos in the laboratory ... it will open a Pandora's box of issues.
"The researchers will not stop. They will want to grow these things," Weldon said.
The White House agreed, issuing a statement Wednesday saying it was "unequivocally opposed to the cloning of human beings either for reproduction or for research."
"The moral and ethical issues posed by human cloning are profound and cannot be ignored in the quest for scientific discovery," the administration wrote.
Other lawmakers planned to offer their own measure, which would ban reproductive cloning yet still allow research.
"The opponents believe once a cell - even if it's a cheek cell - divides in a petri dish, it's a human being," said Rep. James Greenwood, R-Pa.
Rep. Diana DeGette, D-Colo., added, "This is about the right of those living with chronic, debilitating and terminal diseases to get the cures they need to live healthy, productive lives."
Despite the probable passage of a complete cloning ban in the House, it's still unlikely Republicans have the votes to push the measure through the Senate. Republicans control the Senate 51-48-1 but would still need 60 votes to end debate and vote on the bill.
The lack of those votes is what held the bill up in the Senate in the last session.
"I'm confident that a majority of the Senate will reject these unwarranted restrictions on medical research, as it has many times in the past," said Sen. Edward Kennedy, D-Mass., one of the Senate sponsors of a cloning bill that allows research.
By Janelle Carter