The National Park Service has scheduled for tomorrow night a public hearing on the future development of Greenbelt Park, the public campground nearest Washington and a popular regional park.

Park Service plans for the 1,000-acre park inside the Beltway range from doing nothing to spending $1 million to improve present facilities and open the eastern section, 280 acres of woodlands on the east side of the Baltimore-Washington Parkway.

The Park Service may well decide to do nothing, since no funds are earmarked for Greenbelt Park improvements in the next six years, and the park's operating budget has been cut by both the Carter and Reagan administrations.

Although the agency's 142-page report on a study of Greenbelt Park options, released last month, does not mention it, there is another alternative: the Park Service might give up Greenbelt, perhaps turning it over to the state or the bicounty Maryland-National Capital Park and Planning Commission.

The Reagan administration last week denied having a "hit list" of parks it wants to unload, but Park Service officials concede Greenbelt is among several federal facilities that might be transferred. The Park Service already is planning to turn over to the state of Maryland the Baltimore-Washington Parkway, and it recently divested itself of Suitland Parkway by transferring it to the District of Columbia.

Budget restrictions last summer forced the closing of half of Greenbelt Park's 174 camp sites, causing park rangers to turn away hundreds of vacationers. The popular campground may be partially closed again this summer because of budget cuts, according to Park Service officials.

The campsites are used all year. Last weekend more than a dozen families, most from out of state, pitched tents or parked their motor homes in Greenbelt's peaceful pine and hardwood forest.

Cooking breakfast over an outdoor fire, Steve and Lorrie Thrush and their 2-year-old daughter Jessica, from Toms River, N.J., were unhappy to hear Greenbelt might no longer be a federal park.

"If they transferred it to the state or county it might be open to out-of-towners," said Steve Thrush. "It's the closest campground to Washington and for $2 a night, they have everything here, except for showers."

Several pine trees away, Paul and Lawson Bell of Adelphi were striking their tent, as they have done many times at Greenbelt. "We're just out for another weekend of camping. This is a nice place to try out camping gear," said Paul Bell. "But we're upset that the Park Service is cutting back on programs everywhere, here and along the C&O Canal."

The development plans for Greenbelt Park, to be discussed in the public hearing, include the upgrading of trails, roads, camping and picnic sites; the purchase of 10 acres on Good Luck Road adjacent to the south end of the park; underground installation of power lines; establishment of nature trails in the eastern section across the parkway, and construction of new park headquarters.

Cost estimates for the three major alternatives range from $450,000 to just under $1 million, depending on the extent of development. The more expensive options include the addition of athletic fields and trails in the east park and a bike-predestrian bridge over the parkway.

Bicycling has become one of the park's more popular activities. Sunday bike races for all ages were organized last spring by the National Capital Velo Club, one of the nation's largest bike-racing clubs. Nearly 100 bicyclists turned out last Sunday, including novice racers aged 11 to 49.

All options proposed by the Park Service would continue the campground operation. Congress, in establishing the park in 1950, declared as a major purpose the provision of "overnight camping facilities (for) families and groups visiting the nation's capital."

What is now Greenbelt Park was to be the second "Green Town" planned by the Franklin Roosevelt administration to develop moderately priced housing on the rural fringes of the capital. The present city of Greenbelt, completed in 1937 as one of the nation's first planned communities, was never expanded. The unused land acquired by the government was transferred to the Park Service in 1950, when the Baltimore-Washington Parkway was developed.

The hearing is set for 7:30 p.m. tomorrow at the Maryland-National Capital Park and Planning Commission office, 6600 Kenilworth Ave., Riverdale.