A House Appropriations subcommittee, saddled with refereeing several of this year's most difficult environmental battles, moved yesterday to reduce by 21 percent new 1991 timber sales from national forests that provide habitat for the northern spotted owl.

The interior subcommittee took the action amid closed-door maneuvering over a $12.8 billion spending bill that expands to the Florida panhandle and North Carolina an existing one-year moratorium on sales of offshore oil drilling leases. Most of the rest of the U.S. coastline is already covered.

The subcommittee went into executive session to deal with the explosive question of timber operations in federal lands in the Pacific Northwest's old-growth forests. After rejecting a proposal by panel Chairman Sidney R. Yates (D-Ill.) to reduce the size of next year's cut from national forests in Washington, Oregon and northern California to 2.7 billion board feet, members settled on a new figure of 3 billion board feet, down sharply from 3.8 billion this year.

The number was immediately attacked by George Frampton, president of the Wilderness Society, who charged it is still too large to provide protection for either owl habitat or ancient forests.

But members from those areas braced for even harsher criticism from timber interests, plywood plants and unions. Rep. Norman D. Dicks (D-Wash.), a panel member, had lobbied for 3.2 billion board feet.

And subcommittee member Rep. Les AuCoin (D-Ore.) acknowledged that "a lot of people dependent on timber" will be dissatisfied.

"We did our best," he said. "People in our region need to understand we have reached a crossroads. This has been nationalized as an issue."

The lower number was dictated in part by the recent administration decision to list the spotted owl as a threatened species, a status that environmentalists hope will force the Forest Service to take account of owl habitat in authorizing cutting.

But other factors enter into the politics of the issue. Subcommittee member Rep. Ralph Regula (R-Ohio), in proposing a compromise number of 3 billion board feet, warned of the impact of lumber shortages next year on a rebounding housing construction market.

Nationwide, timber sales would drop from 10.3 billion board feet to 9.3 billion next year in the bill.

Yates reserved the right to oppose the higher timber cutting number.

At the same time, AuCoin, in an unusual dissent from the subcommittee chairman's position, reserved the right to oppose a $15 million special allocation to make up a deficit at the Kennedy Center that Yates strongly backs. Arts-supporter Yates suggested that AuCoin's position was purely "tactical."

The subcommittee deferred to the full committee what could be a major fight over offshore oil leasing. Yesterday, Rep. Bill Lowery (R-Calif.) withdrew a proposal to codify a 10-year moratorium on lease sales contained in President Bush's recent proposal.

Instead, the subcommittee expanded bans that already cover most West Coast, Aleutian Basin, New England and southern Florida waters but rejected a request initiated by Rep. Walter B. Jones (D-N.C.) to cancel an old lease to Mobil Corp. off the North Carolina coast.

As the bill moved through the subcommittee, members freely added park, recreation and historical projects for their states or districts.

Rep. Chester G. Atkins (D-Mass.) picked up $250,000 for an Adams National Historical Site in Quincy, Mass., while Rep. John P. Murtha (D-Pa.) restored $1.3 million for the America's Industrial Heritage Project in his district.