After months of phone calls and letters trying to collect thousands of dollars from Horizon Blue Cross and Blue Shield of New Jersey, Dr. Anthony Musarra was fed up.

Late payments from the health maintenance organization were forcing the Absecon, N.J., internist into debt to pay his office expenses, so he asked the state for help.

He was one of more a dozen doctors who accused the HMO of late payments. On June 15, state regulators warned Horizon it could be fined up to $10,000 for appropriate claims not paid within 60 days.

Within days, Musarra said, checks started arriving, and Horizon apologized for the delay. However, Horizon denies allegations about late payments, said spokesman Fred Hillmann. He said the company pays 30 million claims a year and only a few thousand are in dispute.

States are becoming more aggressive in making sure that plans pay claims from doctors and hospitals. Many states have passed laws to specify how quickly HMOs must make payments. States including New York, Florida, North Carolina and Louisiana have started imposing fines.

``When it goes to the state, the plan gets worried and does something about it,'' Musarra said.

Regulators say they're acting to protect patients, noting that some health providers illegally bill patients when an HMO balks at paying. And patients could be hurt if hospitals or doctors have to curtail services because of financial problems resulting from claim disputes.

Barbara Murray of Port Charlotte, Fla., said bill collectors sent by doctors and hospitals hounded her late husband, J.C. Murray, while he was dying of heart disease. The Murrays expected his HMO, Physician Corp. of America (since purchased by Humana), to cover his medical bills but the health plan resisted, saying the Murrays had not paid their premiums on time. The couple denied the charge.

``The last time I took him to the hospital he asked me to sue them, but I never did,'' said Ms. Murray, who eventually paid some of the bills herself.

HMO industry officials defend their record in paying claims on time but say they're not surprised more states are closely scrutinizing payments.

``States are getting more into the micromanagement of health plans in a lot of areas,'' said Susan Pisano, spokeswoman for the American Association of Health Plans.

HMO officials say payments often are delayed because doctors and hospitals make mistakes in filling out claims, or send claims in late.

Florida, Minnesota, Nevada, North Carolina, Colorado, Pennsylvania, Vermont and Virginia have passed laws this year requiring HMOs to pay bills within a certain time or face penalties or fines, according to the National Conference of State Legislatures. In all, 27 states now have HMO prompt-payment bills.

Hospital executives and doctors say the fines are too small to have much impact.

``Getting fined $1,000, what's that do to a large corporation?'' said Sarah Smith, of the Greater New York Hospital Association.

Dr. Clifford Sales, a Westfield, N.J., surgeon, contends that HMOs purposely withhold money to increase profits.

``When my wife called the plumber, he doesn't leave without getting paid, but with HMOs, we are forced to wait and wait and wait,'' said Sales, who filed a complaint with New Jersey regulators claiming about $52,000 in overdue payments from Oxford Health Plans.

Oxford, whose claims-paying ability has come under scrutiny in New York and New Jersey, acknowledges it had problems paying bills on time a year ago but says it resolved them.

Oxford has paid $71,100 in fines this year to the New York Insurance Department.