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Gov. Mitt Romney (search) vetoed a bill Friday that would expand embryonic stem cell research (search) in Massachusetts, but the measure has more than enough support in the Legislature to override the governor's veto.

Romney supports research using adult stem cells or leftover frozen embryos (search) from fertility clinics. But he opposes the legislation because it would also allow therapeutic cloning (search), in which scientists create a cloned embryo to harvest stem cells in hopes of using them to treat and cure disease.

Critics have said the practice amounts to creating human life only to destroy it.

"It is wrong to allow science to take an assembly line approach to the production of human embryos, the creation of which will be rooted in experimentation and destruction," Romney said in a letter to lawmakers explaining the veto.

The Republican governor had appealed to the Democrat-controlled Legislature to amend its original bill and ban the cloning (search) measure. He also urged lawmakers to include language defining the beginning of life as the moment of conception, banning the production of human embryos for other research purposes, and limiting compensation to women who donate their eggs.

But the Legislature rejected all four amendments, leading to Romney's largely symbolic veto.

"I could not in good conscience sign a bill of this nature," he told reporters on Friday.

The House and Senate passed the bill with veto-proof margins, and both chambers were expected to vote next week to override the veto.

A spokeswoman for Senate President Robert Travaglini, who introduced the bill, had no immediate comment.

Under existing state law, scientists who want to conduct embryonic stem cell research first need approval of the local district attorney. The bill would remove that requirement, give the state Health Department some regulatory controls and ban cloning for reproductive purposes.

Romney's opposition puts him at odds with some of the top university and research facilities in Massachusetts, including the newly formed Harvard Stem Cell Institute. Researchers there are looking to compete with institutions in California, where voters last year approved a $3 billion bond to fund a stem cell research agency.

California and New Jersey already allow therapeutic cloning. California voters approved a plan last year to spend up to $3 billion over the next decade to foster the research.

Stem cell research has become an issue nationally as well, as a bill lifting limits on stem cell research makes its way through Congress.

The House approved the bill, which does not allow therapeutic cloning, by a 238-194 vote on Tuesday, and the Senate is expected to take it up. President Bush has promised a veto.

"What our Legislature has done goes well beyond what was done in Washington," Romney said.