Backers of a ballot question allowing terminally ill patients to request and self-administer life-ending medications say they have gathered enough valid signatures to put a binding question before voters in November, and are now bracing themselves for a fight with the Catholic Church and several other organizations.

The Boston Archdiocese, the Massachusetts Medical Society, the Massachusetts Family Institute, Massachusetts Citizens for Life, and some advocates for the elderly and disabled, have all indicated plans to mount a vigorous campaign to defeat the proposal, contending it is fraught with the potential for error and could be used to compel older, ill adults to end their lives.

With a second and final signature deadline nearing, the Death with Dignity campaign collected more than 21,000 signatures – almost double the amount they need to place the question on the Nov. 6 ballot. Supporters say polls show overwhelming support among Massachusetts voters to allow terminally-ill adults to legally request medication from their doctors to end their lives.

If voters pass the ballot question, Massachusetts would become the fourth state to legalize doctor-assisted suicide, along with Oregon, Washington and Montana.

The proposal lays out parameters for terminal patients to receive life-ending medication. To qualify, a patient must be a Massachusetts resident who is diagnosed by two physicians with an incurable disease that will cause death within six months. Doctors must determine the person is mentally capable of making and communicating health care decisions, and are required to inform patients about other end-of-life care options, including palliative and hospice care.

In a poll taken by the Western New England University Polling Institute, 60 percent of voters supported physician-assisted suicide, 29 percent opposed it. The poll was conducted in late May with 504 voters.

According to the institute, 52 percent of all Catholic voters said they support the idea, 36 percent oppose it and 12 percent said they did not know or declined to answer. Among Catholic voters who attend church at least once a week, 52 percent opposed the death-with-dignity proposal and 37 percent supported it.

Despite the favorable polls, backers of the physician-assisted suicide ballot question say it is going to be a fight to get it passed in Massachusetts. The proposal is based on a similar law in Oregon that has been in effect for 15 years.

“I think it is going to be tough because the Catholic Church is so strong in Massachusetts and for them this is just a religious matter,” said Dr. Marcia Angell, one of the original sponsors of the initiative petition. “I am not sure Catholics who are not in the hierarchy will go along with the church’s position.”

Several months ago, the Boston Archdiocese launched a campaign to fight the doctor-assisted suicide question, putting posters and pamphlets in churches, creating pew cards and a website, suicideisalwaysatragedy.org. The Massachusetts Catholic Conference, the public policy arm of the church, is actively advocating against the ballot measure.

“The Catholic Church, like many in the medical and psychiatric community, is fundamentally against facilitating suicides of any kind. We have particular concerns with the flaws in this petition, which, for instance, does not require patients to seek psychological evaluation before ending their lives,” James Driscoll, executive director of the Massachusetts Catholic Conference, said in a statement to the News Service. “In recent years, hospice and palliative care professionals have made enormous strides in alleviating pain and suffering. We believe the Commonwealth would be better served by investing in these chronically underfunded programs.”

Last fall, when Attorney General Martha Coakley certified the petition, Cardinal Sean O’Malley gave a homily on the subject, saying “suicide is a tragedy, one that a compassionate society should work to prevent” by focusing more on care for the terminally ill. He went on to say allowing doctors to prescribe life-ending medication is a “corruption of the medical profession.”

The Massachusetts Medical Society, which represents 23,000 doctors and medical students statewide, has a policy against physician-assisted suicide, according to Dr. Richard Aghababian, president of the society.

“There is a longstanding tradition in medicine to keep people alive, not to end their lives. That is not our role,” he said.

Aghababian said many doctors might have a problem with the six month demarcation for a person to receive life-ending drugs. It is not easy to predict when someone will die, he said.

“If someone is able to be with their family, we don’t feel is our duty to take that six months away from them. I know it is a personal issue. We are here to preserve life to the extent of our ability. We are not here to take it,” Aghababian said.

Angell, trained in internal medicine and pathology and the former editor of the New England Journal of Medicine, disagreed, saying it is a doctor’s responsibility to relieve suffering.

“This isn’t about doctors. This is about patients. It is the patient’s needs we should be focused on and not doctors’ abstract notions about their roles,” she said.