WASHINGTON (AP) - Visits to emergency rooms are booming even as hospitals are closing, raising fears that some patients may not get urgent care as fast as they need it, the American Hospital Association reported Thursday.

The report comes as no surprise to many cities that for more than a year have reported ER crowding so bad that hospitals routinely divert ambulances to competing emergency rooms. The situation reached a crisis last winter when ERs around the country overflowed with flu patients.

But the hospital trade group suggests the crowding may only worsen because of financial problems. Federal law requires hospitals to care for patients who come to emergency rooms. But there is no federal program to reimburse hospitals for the care of poor, uninsured people. Additionally, Medicaid reimbursement is low for emergency services and managed-care plans sometimes deny payment for ER visits, the report says.

Emergency room visits rose by 15 percent in the 1990s, hitting 99.5 million in 1999, the AHA reported. One of every five Americans has been to the ER at least once, visits accounting for 40 percent of all hospital admissions, the report says.

Yet the number of emergency departments dropped as 493 hospitals, particularly in rural areas, closed between 1990 and 1999, the report says.

Also, existing hospitals have cut the number of beds. So if intensive care beds are full, those patients stay in the emergency room, which can't accept as many incoming patients - the main reason for ERs diverting ambulances to other hospitals, the report says. It cited an informal survey suggesting two-thirds of hospitals ordered ambulance diversions in the last year.

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