WASHINGTON — A quiet revolution is transforming the way medical care is delivered in this country, and it has very little to do with the sweeping health care legislation that President Barack Obama just signed into law.

Traditionally, American medicine has been largely a cottage industry. Most doctors cared for patients in small, privately owned clinics — sometimes in rooms adjoining their homes.

But an increasing share of young physicians, burdened by medical school debt and seeking regular hours, are deciding against opening private practices. Instead, they are accepting salaries at hospitals and health systems. And a growing number of older doctors — facing rising costs and fearing they will not be able to recruit junior partners — are selling their practices and moving into salaried jobs, too.

As recently as 2005, more than two-thirds of medical practices were physician-owned — a share that had been relatively constant for many years, according to the Medical Group Management Association. But within three years, that share dropped below 50 percent, and analysts say the slide in physician ownership has continued.

For patients, the transformation in medicine is a mixed blessing. Ideally, bigger health care organizations can provide better, more coordinated care. But the intimacy of long-standing doctor-patient relationships may be going the way of the house call.

And for all the vaunted efficiencies of health care organizations, there are signs that the trend toward them is actually a big factor in the rising cost of private health insurance. In much of the country, health systems are known by another name: monopolies.

Behind the trend

The trend away from small private practices is driven by growing concerns over medical errors and changes in government payments to doctors. But an even bigger push may be coming from electronic health records. The computerized systems are expensive and time-consuming for doctors, and their substantial benefits to patient safety, quality of care and system efficiency accrue almost entirely to large organizations, not small ones. The economic stimulus plan Congress passed early last year included $20 billion to spur the introduction of electronic health records.

For older doctors, the change away from private practice can be wrenching, and they are often puzzled by younger doctors’ embrace of salaried positions.

“When I was young, you didn’t blink an eye at being on call all the time, going to the hospital, being up all night,” said Dr. Gordon Hughes, chairman of the board of trustees for the Indiana State Medical Association. “But the young people coming out of training now don’t want to do much call and don’t want the risk of buying into a practice, but they still want a good lifestyle and a big salary. You can’t have it both ways.”

Dr. Mirro’s story

Dr. Michael Mirro, of Fort Wayne, Ind., is among those caught in the tide. A 61-year-old cardiologist, he began his career like so many of his peers in a small private practice with two other cardiologists. They gradually added doctors until, by last year, they had 22 cardiologists, making theirs one of the largest private heart clinics in Indiana.

But in December, Mirro and his partners sold everything to Parkview Health, a growing health system that owns the hospital across the street from their building. “We had to hire more and more people to contact insurers and advocate for people to get the care they needed,” Mirro said. “That’s expensive.” As insurance rates rose and coverage weakened, patients were forced to pay out of their own pockets an increasing portion of Mirro’s bills. When the economy soured, many stopped trying.

“In the last year, the share of our patients from whom we could not hope to collect any money rose to about 30 percent,” Mirro said. He and his partners had been thinking of selling for years. But they made the decision after the Centers for Medicare and Medicaid Services decided last year to cut reimbursements to cardiologists by 27 to 40 percent, depending on the type of practice. The Medicare savings in cardiology are to be used to pay more to primary care doctors, widely seen as under great financial strain.

Although Mirro saw his decision as life-changing, many of his patients noticed little difference. Parkview let the doctors remain in their building and allowed them to continue to hire their own staff.

Mimi Strong, an 89-year-old heart failure patient, said everything was the same when she visited recently. Told in an interview that her care may now be more coordinated, Strong expressed little interest.

But it matters to Mirro. “We wouldn’t go back,” he said, “now that we’ve seen the value of improved patient care and improved communication with primary care physicians.”