The Reagan administration has ordered a review of more than 100 land-acquisition plans for national park lands and forests as part of a move to allow larger parts of them to remain under private ownership.

Under the policy, "land-protection plans" will replace the existing "land-acquisition plans" to guide additions to National Park Service, Bureau of Land Management, Fish and Wildlife Service and Forest Service properties.

The change has pleased "inholders," those who own land within the federal enclaves and who in the past have been threatened by government moves to take their land through eminent domain proceedings. But the new policy concerns environmental groups and members of Congress who want the Interior Department to continue purchasing park lands.

Specifically, the policy calls for federal land managers to "use to the maximum extent practical cost-effective alternatives" to buying private land. When acquisition is necessary, the policy says, managers should "acquire or retain only the minimum interests necessary to meet management objectives."

Ric Davidge, the Interior official who chaired the group that wrote the six-paragraph policy, said there are dozens of ways a natural area can be protected without purchasing the land. The alternatives include exchanging parcels with inholders, paying them for the use of their land as easements or rights-of-way and making informal agreements with property owners on how their land will be used.

"Historically, most lands have been purchased at full fee, and that's costing us . . . unnecessary expense," said William F. Hartwig, staff director for Interior's land policy group. "Using this new policy we can protect more land for less money. We're not willing to compromise the protection of these areas for a lack of money."

Davidge served as managing director of the National Inholders Association and director of government affairs for the National Property Owners, both park property owner groups, before coming to Interior last year. Most of the 75 public comments on the policy were Mailgrams from inholder groups around the country.

Charles S. Cushman, chairman of the 6,000-member inholders association, said, "The national park system was being turned into the private playground" of congressmen like Rep. Phillip Burton (D-Calif.) and Rep. John F. Seiberling (D-Ohio), who have promoted park-land purchases. "This reverses the trend."

Typical of those who filed supporting comments was Tim Ray of the Eugene (Ore.) Land Owners Association. "Your new land-protection policy is music to my ears," he said. "This will help resolve a lot of built-up hostilities in the federal government land grab."

But some environmental groups took a different view. "It is one thing to be flexible, innovative, efficient and economical, and it is quite another thing to shut down the store and go out of the land-acquisition business altogether with an unfinished agenda," said Martin J. Rosen, president of the Trust for Public Land. "We fear that is where the . . . policy is headed."

The National Wildlife Federation and the National Audubon Society also opposed the change.

Seiberling said that "in principle" he had no objection to the plan. But, he said, "The difficulty comes when you try to apply it evenly to every situation."