The Southern Maryland Hospital Center in Clinton has been forbidden by a state health planning commission to use half of a new addition until it obtains the state approval it was required to seek for construction.

It also was ordered to donate $25,000 to a charity as punishment for violating state planning rules, which were designed to hold down health care costs by assuring that only needed facilities are built.

The Maryland Health Resources Commission also barred the hospital from charging patients higher prices to help recover the cost of the addition or the donation to an unspecified health charity.

Taking its first enforcement action since it was created in 1982 to oversee hospital construction, the commission found that the hospital owned by Dr. Francis B. Chiaramonte had "undermined the integrity of the health planning process."

Commission Chairman Carville Akehurst said in a letter to Chiaramonte Feb. 5 that "the controversy and its cost to Southern Maryland Hospital Center, the commission and the health care system could have been avoided by a simple phone call or a short letter before the hospital started its building . . . . "

Richard Coughlin, director of the commission's nine-person regulatory staff, said the hospital signed a 10-page consent decree acknowledging it had violated state "certificate of need" rules and agreeing to the penalties. Hospital officials did not return a reporter's phone calls yesterday.

In 1984, the 308-bed hospital was granted a certificate to add 37 more beds. The hospital then added two floors to an adjoining warehouse, Coughlin said, but the commission contended it had authority to add only one.

Southern Maryland Hospital officials argued that state permission wasn't needed because each floor was built under a separate contract for less than $600,000, the minimum expenditure over which the commission has authority. Because the entire addition cost $835,000, the commission said, a new certificate of need was required.

In taking action against the hospital, the commission rejected its staff's recommendation to rescind approval of the 37-bed addition. That approval was opposed by competitors of the Southern Maryland hospital, Prince George's Doctors Hospital and the Fort Washington Community Health Center, and has been appealed to the courts, Coughlin said.

Coughlin noted that Southern Maryland has a "pretty high" occupancy rate compared with other hospitals in the state. From July 1, 1974, through June 30, 1985, it had a daily average of 276 patients, or 89 percent of capacity, compared with 374, or 68 percent of capacity, in the 550-bed publicly owned Prince George's General Hospital.