The hospitals must still prove to federal regulators that their merger would not be an illegal monopoly, and win approval from the state Health Department and the attorney general. But if they succeed, a united Lifespan and Care New England would become not just the biggest health-care organization in the state, but the biggest company of any kind doing business chiefly in Rhode Island. Its annual patient revenues would approach $2 billion; its employees would number 17,600.

Lifespan encompasses the state’s biggest hospital, Rhode Island Hospital, as well as Miriam Hospital, also in Providence, Bradley Hospital, a children’s psychiatric hospital in East Providence, and Newport Hospital.

Care New England consists of Women & Infants Hospital, in Providence, where the majority of Rhode Island babies are born; Kent Hospital, in Warwick; and Butler Hospital, a psychiatric hospital in Providence.

All the hospitals are not-for-profit.

The new organization would be called Lifespan and Vecchione would remain as CEO. Hynes would become senior vice president for special projects.

The combination would bring together five of the seven hospitals affiliated with the Warren Alpert Medical School of Brown University, coming closer to creating the “academic medical center” that Brown has long craved.

But the six hospitals left out of the new Lifespan include the most financially vulnerable in the state. Every one of the six lost money last year, and Landmark Medical Center in Woonsocket is amid a particularly deep financial crisis. How the merger will affect those hospitals’ viability is likely to be a top concern for regulators.

Vecchione revealed that Lifespan is “having exploratory discussions” about acquiring Landmark. The decision will hinge, in part, on whether Landmark would increase Lifespan’s market share enough to breach antitrust laws.

As the news of the merger, rumored for weeks, began to eke out today, reaction was wary and restrained.

The state’s two largest health insurers, which could face tougher negotiations over reimbursement rates with a united hospital system, both said it was too soon to comment.

Dr. Barry Wall, president of the Rhode Island Medical Society, called the merger a symptom of problems in the health care system. “This looks like it’s going to change the landscape. I think a change in landscape is a sign of trouble,” Wall said. “I don’t think beyond that anybody can say anything.”

Michael Healey, spokesman for Attorney General Patrick C. Lynch, whose office must approve the merger, said that Lynch “believes that although these institutions are extremely important, they’re still not as important as the people they serve.” Healey noted that “a ton” of work remains to be done before the merger can go through.

Rick Brooks, director of the United Nurses and Allied Professionals, the union that represents 2,000 nurses and technical workers at Rhode Island Hospital, said that the merger would require greater accountability by the hospitals.

“These hospitals really belong to the people of Rhode Island,” he said. “They don’t belong to any one person or any one company.”

Louis R. Giancola, president of South County Hospital, one of the community hospitals that will not be part of the new Lifespan, said it was too soon to predict what effect the merger would have on his institution. But he agreed with Wall that it was a sign of trouble.

“It demonstrates how challenged community hospitals, including Kent, are -- that this kind of combination is necessary to be able to continue to serve their community,” Giancola said.

Kent, which is part of Care New England, has been struggling financially and some observers see the merger as an attempt to rescue Kent.

Hynes, however, said that merger would not involve infusions of cash to Kent, and that Kent was expected to improve through administrative changes already under way.