Jim Kalp lives in a four-bedroom frame house on 2,000 acres of parkland in southern Prince George's County.

His rent: $100 a month.

Kalp, 41, is a maintenance worker for the Maryland-National Capital Park and Planning Commission and one of 30 tenants -- 24 of them park employees -- of the agency in Prince George's County. The average rent is $143 a month. Three tenants pay no rent.

"This is great, just what we were looking for," Kalp said of the 1903 tenant farmhouse. "I don't know what we'll do when we have to leave."

The rental rates may violate both federal tax rules and the regulations of the park agency, which since 1985 has required market-rate rents and annual rent increases. In Prince George's, there have been no increases in years.

After inquiries by The Washington Post, John W. Rhoads, head of the Prince George's park and planning board, ordered his staff recently to raise the rents, a process that will take months.

For many tenants, that could mean substantial increases, according to Jacqueline Gilbert, who manages the rental properties. For instance:

Joseph Dunning, a retired park employee, and his wife, Mary, both in their nineties, pay $35 a month for a Colmar Manor cottage. A 1986 appraisal said the market rent was $350.

Park employee Don Graham, 33, lives in a three-bedroom addition to the 18th-century Montpelier Mansion in Laurel, where he works as the $25,000-a-year caretaker, curator and tour guide. His rent: $100 a month, compared with the 1986 appraised rent of $750 a month.

The Prince George's rents contrast sharply with those charged to park commission tenants in Montgomery County, where park employees pay $450 to $1,200 a month to live in some of the 80 houses the agency leases. The commission oversees parkland in both counties, but each has its own staff and policies.

Before Rhoads ordered a change in policy, Prince George's officials strongly defended the low rents, saying they reflected a "difference in philosophy" with Montgomery. They said some of their tenants are elderly or poor and raising their rents could make them homeless, while others are park workers providing security and maintenance.

Many of the houses came with property the agency acquired for future parkland. In Prince George's, the agency owns 18,000 acres; in Montgomery, 27,000 acres.

Montgomery has its properties regularly appraised and raises rents every July 1. Park employees get a 7 percent break because of administrative saving from having their rent paid through payroll deductions. They receive another reduction of up to 5 percent for "nuisances" associated with living on parkland.

The Montgomery County arm of the park agency adopted its rental policy after an Internal Revenue Service investigation. Montgomery County had to pay the U.S. government $78,000 in 1977 after the IRS determined that the lower rents were a taxable benefit. Montgomery thereafter raised rents.

Prince George's park officials declined to comment on the tax issue. Gilbert referred a reporter to Ed Navarre, the bi-county agency's secretary-treasurer.

"If, in fact, the rents are below market, the commission would be liable to withhold taxes on the difference," he said. "The tax implications are if IRS comes in, the employees are liable. Certainly, the commission would pay it and decide whether to go after the employees. In Montgomery, they did not."

Ronald D. Schiff, commission general counsel, said Montgomery park officials "are very, very sensitive that they're not tainted with the same brush" as Prince George's. "They've instituted rules, had them in effect for years."

Gilbert said Prince George's park employees will still get a rent reduction for services provided, but how much remains to be seen. The matter will be brought to the county park and planning board for a vote, she said. Until now, the staff has set the policy.

"If we had our druthers, we'd like to see the houses eventually demolished except for historic properties, because we don't want to get into the landlord-tenant rental business," said Robert M. Arciprete, chief of park planning and development. "Many times, if it's a sharecropper, we don't want to tear down a house because these people could be homeless."

That ambivalence about being a landlord has sometimes resulted in seemingly contradictory treatment of tenants. Jeff Adams, 30, lives in a dilapidated park-owned house on a dirt road in Aquasco. He has no phone and no indoor plumbing. He has lived in the house his whole life and says he would like to buy and improve it.

"They were tenant farmers working for the previous owner. And as part of the purchase deal, they were allowed to stay," Gilbert said. "Mr. Adams died, and I was informed Mrs. Adams lives almost full time with a daughter in Washington. The deal was not with the son . . . . He has been allowed to live there this summer."

But the commission installed indoor plumbing in the nearby farmhouse where Kalp, the maintenance worker, lives with his family. The Kalps then moved into the house in February 1987. Even without running water, the appraised market rent was $150, 50 percent more than the Kalps pay.

Michael Wynnyk pays $75 a month to live with his family in a historic two-bedroom house near a county-owned golf course. "I've put in a lot to fix it up," said the 35-year-old park police officer, who is paid $35,000 a year.

Wynnyk says the low rent allows him to save for a down payment on a house. "It gives you an opportunity to get it together and move on," he said. "I guess it's one way they help their employees out."