The Interior Department's inspector general has opened an investigation into whether National Park Service officials were pressured into allowing Washington Redskins owner Daniel Snyder to cut more than 130 mature trees last fall from a slope behind his Potomac estate.

Scott L. Culver, deputy director of the Program Integrity Division in the department's Office of the Inspector General, said a probe was launched recently after his office received a formal complaint.

"We initiated an inquiry into all of it," Culver said. "We are really just looking to see if the proper procedures were used and whether there was any undue influence put upon the Park Service."

Culver, whose office investigates allegations of fraud or mismanagement within the agency, would not comment further. The Interior Department manages the Park Service.

In November, the Park Service granted Snyder permission to clear 50,000 square feet of forested land on a protected easement he owns along the C&O Canal. Under the agreement, Snyder was allowed to cut down the trees in exchange for a possible share of the enhanced property value he might receive from his new view.

The decision, which outraged some neighbors and environmentalists, prompted accusations that the Park Service was effectively selling views of the Potomac.

Snyder did not return a phone call to his spokesman yesterday.

Kevin D. Brandt, superintendent of C&O Canal National Historical Park, who negotiated the deal with Snyder, could not be reached to comment. Bill Line, a spokesman for the Park Service's National Capital Region, did not return calls to his home or office.

Meredith Lathbury, an attorney for the Potomac Conservancy, praised the investigation.

"I think everybody who has looked at the facts of this case had thought that something smelled funny," said Lathbury, who said she was contacted this week by an Interior Department investigator.

Park Service officials have offered conflicting statements about the deal since it was first publicized in December.

Initially, they indicated that the trees were cut by mistake. Later, however, they conceded that Snyder was allowed to cut down 130 trees to rid his property of nonnative species that the Park Service has been trying to keep out its forests.

In exchange, the Park Service negotiated future additional protections on the 8.3-acre easement, which the government purchased in the 1970s.

Snyder was also to hire an appraiser to inspect his $10 million estate and determine its value with the new view. If the value exceeded the additional protections that the Park Service received, Snyder was to donate the difference to the federal government.

But the agreement has been suspended pending the outcome of Montgomery County's investigation into whether Snyder violated local forest conservation laws by removing the trees without the approval of the planning board. Planning officials and Snyder are negotiating the terms of a possible settlement.

Last month, Lathbury and attorneys for the Audubon Naturalists Society said they think the Park Service violated federal law by failing to get public input before issuing the tree-clearing permit to Snyder.

Under the National Environmental Policy Act, federal agencies must consider the environmental impact of proposed activity on federal land. For the Park Service, that means producing an environmental assessment and giving public notice, neither of which occurred in the Snyder case.

Park officials, citing an exemption for the removal of invasive species, said the Snyder case was exempt from the act. The environmental attorneys, who note that Snyder was allowed to cut 20 native trees, disagreed.

"We are hoping the [Interior Department] investigation will lead to the Park Service actually going through the proper regulations," Lathbury said.

Staff researcher Bobbye Pratt contributed to this report.