Governor Mitt Romney set off a storm of criticism Thursday after he declared in a published interview that he favored banning a specific type of stem-cell research. Scientists and the leader of the state Senate accused him of trying to block a promising avenue of research, even as anti-abortion groups assailed him for declaring that he did not object to stem-cell research involving embryos from fertility clinics.

Romney took aim at stem-cell research being planned at Harvard University, where embryos created by cloning would be used.

The governor said that he opposes "the creation of new human embryos for the purpose of research" and his aides indicated he would support criminal penalties for researchers who use new human embryos.

The governor's position was published Thursday in a New York Times article and was immediately interpreted by political analysts and some Beacon Hill politicians as an attempt to tack rightward as he eyes a possible presidential run in 2008. Romney and his aides, however, characterized it as a response to the fast-changing world of stem-cell research.

Romney has described himself as a supporter of embryonic stem-cell research since he ran for governor in 2002, and, as recently as last month, he said he would support the Legislature's efforts to promote such research in Massachusetts. But in a letter he sent to Senate President Robert E. Travaglini on Thursday, Romney said that, "respect for human life is a fundamental element of civilized society" and that "lofty goals do not justify the creation of life for experimentation and destruction."

The governor's remarks prompted Travaglini to call a news conference to criticize the governor's approach. The provost of Harvard also complained in an interview that Massachusetts could lose ground in the competition that has erupted among scientists, politicians, and private companies since California voters passed a $3 billion initiative for stem-cell research last fall.

"We are very concerned that this will create a symbolic advantage for California," said Harvard provost Dr. Steven E. Hyman. In a hastily convened news conference at the State House, Travaglini and leading stem-cell researchers said the governor's approach would diminish the chances of finding cures to dreaded diseases.

Travaglini said he wants to send a message that the medical industry is welcome in Massachusetts. "I'm disappointed that the governor has decided to send the opposite message. Rather than endorsing stem cell research, he is raising fears and unfounded doubts," he said.

"I believe that there is the potential for significant medical breakthroughs, the realization of a cure for young children with juvenile diabetes, spinal cord injury, people with Alzheimer's and Parkinson's," Travaglini said. "I believe we can put in place, and I'm confident this will be the result of the process, the necessary safeguards to ensure that this type of research is supervised and properly monitored." Dr. George Q. Daley, a stem-cell researcher on one of the Harvard teams, explained at Thursday's news conference that creating stem cells through cloning makes it much easier for scientists to study specific diseases and, perhaps, find cures for individual patients.

Cloning allows researchers to create stem cells with the DNA of patients who suffer a particular disease, giving them a new way to study the development of the disease in the laboratory. In theory, cloning could also allow scientists to create embryonic stem cells, and then replacement tissues, which have the DNA of a patient, meaning that the tissue will not be rejected by the body.

"It creates cells that are identical to the patient you hope to treat," Daley said. "It allows us to move a genetic, or misunderstood disease, into the petri dish so we can study it. And it also gives us unique tools for treating an invidivual patient in an highly effective and safe way."

Travaglini's aides were privately incensed Thursday because they said Romney did not alert them to his plans to announce his position and appeared to upstage Travaglini. The governor's remarks surfaced the day after Travaglini filed his own stem-cell bill, which would give the state's endorsement to more types of stem-cell research than Romney's approach.

There are two types of stem cells: adult stem cells, which are already used to treat some diseases, and embryonic stem cells, which are not used to treat diseases but are easier to work with in the laboratory and are able to become a much wider range of cells. Scientists hope to use stem cells to repair tissue damaged by disease and injury.

Most human embryonic stem cells used today were created from embryos left over from fertility treatments.

Romney said although he supports the use of embryos left over from in vitro fertilization, which might be discarded anyway, he opposes the creation of embryos by cloning. Travaglini filed a bill Wednesday that would allow both, but would ban the creation of cloned human babies. President Bush has barred the use of federal money to create any new batches of human embryonic stem cells, restricting researchers to the use of existing stem cell lines.

Romney's aides said he may propose his own bill, depending on what comes out of the Legislature. If he does file his own bill, it could include criminal and civil penalties for research using cloned human embryos.

Travaglini said Romney's decision to reveal his position in The New York Times lends credence to the idea that he is using the stem-cell issue to nurture his national ambitions. "There's evidence that is clearly concerned with the national agenda," Travaglini said. "One could argue this is consistent with that evidence."

Jeffrey Berry, a political science professor at Tufts University, said Romney's use of a national newspaper to reveal his position on a Massachusetts policy issue is a clear sign that he is trying to position himself for the Republican presidential primaries. Berry said Romney is aiming to soften his liberal image among the socially conservative voters who dominate those contests.

"It is a sign he is not concerned about Massachusetts as we would expect a sitting governor to be," Berry said. "He is speaking to a national audience."

Romney scoffed at the idea that his interview with The New York Times has anything to do with presidential ambitions. Saying he regularly reads The Note, ABC's daily political newsletter, he argued out that local and regional media outlets are just as accessible to a national audience in the age of the Internet.

"I don't think there is any such thing as the national media today, and the local and regional media," Romney said. "I read the Note everyday. There is no story that I know that is a local story that is not a national story."

Romney said Thursday that his position has evolved with the times; the Globe reported last October that two teams of Harvard researchers were preparing to work with embryos created through cloning.

"I didn't ask President Travaglini to make stem-cell research his first priority. Interestingly, last year, I supported what he was looking for. But this new dimension, which is creating new embryos through cloning, this is a very new line, and I would not cross that line," Romney said Thursday.

Romney said he reached his decision after meeting with researchers, ethicists and advocates and discussing the issue with his wife, Ann. Ann Romney has multiple sclerosis, a disease that stem-cell research might one day help to treat. He did not elaborate on his wife's condition Thursday.

If Romney was attempting to impress social conservatives, his effort fell flat. Massachusetts Citizens for Life and the Massachusetts Catholic Conference, which have lobbied heavily against the Legislature's previous efforts to approve stem-cell bills, said they oppose the governor's stance because they believe a human embryo is a human being that should not be destroyed, even if it is left over from in vitro fertilization. The National Right to Life Committee, a prominent Washington-based group, agreed.

"I'm not sure there is a lot of difference. If you are taking the stem cell from the embryo for research, you have to destroy the embryo. He's still in favor of killing the new lives that are in existence right now," said Carol Tobias, the group's political director. "If that embryo, that human life, is being destroyed for the research, that is not proper. That is not ethical."

Gareth Cook of the Globe staff contributed to this report.