Hospitals in Washington's Maryland suburbs are in the midst of their largest construction boom in a decade, according to figures recently compiled by the Maryland Health Care Commission.

The spike in hospital expansion and renovation, part of a regional and national trend, comes after years of predictions that managed care would shrink demand for hospitals by steering patients to smaller neighborhood clinics.

Instead, a largely unanticipated increase in people going to hospitals, particularly emergency rooms, has spurred the projects, hospital administrators said.

"Many hospitals . . . were built around the same time, post-World War II, and it's time for renovations. But in doing the renovations, you're also seeing a lot of new expansion," said Nancy Fiedler, spokeswoman for the Maryland Hospital Association. "A significant portion of Maryland hospitals have either undergone major construction in the last five years or are planning to do so soon."

In fiscal 2000 and 2001, Maryland hospitals reported to the state that they planned to spend $360 million and $278 million, respectively, on construction, according to numbers compiled by the Health Care Commission. Those figures eclipsed the next-largest amount spent in a single year over the previous decade -- $265 million in 1991.

Every year, hospitals report planned construction to the state in applications for "certificates of need," a mechanism that allows Maryland to regulate the projects based on public demand. In April, the commission issued a report indicating a surge in hospital construction in 2000 and 2001. At a reporter's request, the commission recently compiled the past decade of application numbers, which provided new indication of an unprecedented level of construction.

In fiscal 2002, there was a dip in construction spending among the state's 46 acute-care hospitals, with a total of $97 million. But with many of the projects approved in the previous two years fully underway, the building boom is just now becoming visible, hospital administrators and state officials said.

Much of the construction focuses on expanding emergency rooms, which are increasingly crowded throughout the state, officials said.

Two Southern Maryland hospitals, for example, are in the middle of doubling their emergency department capacity. Southern Maryland Hospital Center, in southern Prince George's County, broke ground in September on a project that will double the size of its emergency department.

St. Mary's Hospital in Leonardtown started a $24 million expansion in February. That project will double the hospital's emergency room space and is expected to be finished late next year, said spokeswoman Martha Beavers.

A year ago, Anne Arundel Medical Center opened a $65 million, 277,000-square-foot acute-care center, and it is in the process of a $13 million expansion of another building.

Howard County General Hospital opened a $12 million, 24,000-square-foot emergency department in July, tripling its emergency room space. In 1990, the hospital had about 24,000 emergency visits a year. Last year, it had 56,000.

Growth in patient numbers has "just gotten incredible," said Mary Patton, spokeswoman for Howard County General. "The entire community has grown in the last 30 years by incredible numbers, and really we're just trying to keep up."

Even in more established, slower-growing counties, construction is booming.

All five of Montgomery County's community hospitals have major expansions underway or planned, including a 30,000-square-foot, 24-hour satellite emergency room in Germantown.

In January, Prince George's Hospital Center will begin the first phase of a four-year, $12 million project that will include an expansion of the hospital's maternal and child health care unit and the neonatal intensive-care unit.

The problem of emergency room crowding became acute nearly a decade ago at Baltimore hospitals but recently has shown up in Montgomery and Prince George's counties and even Washington's outer suburbs, said Robert Bass, executive director of the Maryland Institute for Emergency Medical Services Systems.

The frequency of "yellow alerts" at emergency rooms has risen steadily across the state in recent years, data show. The alerts, issued statewide by hospitals when their ER beds are full, are expected during flu season but have become commonplace throughout the year, Bass said.

When a hospital goes on yellow alert, ambulances are asked to divert patients to other hospitals unless a person has a life-threatening condition.

"Even hospitals in rural areas are experiencing yellow alerts," Bass said. "That's a problem because the next hospital may be 30 or 40 minutes up the road."

New emergency room space can help ease crowding in the short run, Bass said, but the new buildings tend to fill up not long after they are built. "We've got all of these factors converging -- sicker people, crowded hospitals, a nursing shortage -- so the net result is that even when you build a larger ER, it just fills up," he said.

In recent years, two trends began catching up to the drop in hospital admissions that had been induced by managed care, hospital administrators said. A growing demand for specialty health care from aging baby boomers and an increase in the number of people without reliable primary care resulted in a spike in emergency department admissions.

For people who can't get in to see their primary care doctor or who don't have one, the emergency room becomes the first and last resort.

And with pressure from managed-care organizations to reduce the number of patients admitted to hospitals for overnight stays, many end up staying in the ER for much longer, said James J. Scheulen, administrator of emergency departments at Johns Hopkins University hospitals.

"Ten years ago, when someone came in with an asthma attack, we would give them two or three treatments and if it didn't work, we would admit them" to the hospital, Scheulen said. "Now, we have to keep them and give them five treatments, six treatments, eight treatments, and we end up keeping the patient in the emergency department for eight hours."

Anne Arundel Medical Center opened an acute-care center last year and is expanding again.