The Senate left town last night, for all practical purposes, postponing action on the Alaska lands bill until after the Democratic National Convention.

Only routine tasks are scheduled to be performed today, with no votes planned, in the wake of a grueling session over Alaska. Senate Majority Leader Robert C. Byrd (D-W.Va.) finally filed a cloture petition to shut off debate when he could not get the measure's lone opponent to shut up.

Sen. Mike Gravel (D-Alaska) out-maneuvered Byrd and everyone else with repeated quorum calls and procedural motions on the bill's complex time agreement, which had specifically been designed to avoid a Gravel filibuster. Gravel opposes any Alaska legislation, and played to galleries full of Alaskans who supported him in that feeling.

But the rest of the Senate was eager to vote on the measure, which has been pending one way or another for four years. It would put various chunks of Alaska totaling more than 100 million acres into several categories of wildlife and environment protection, balancing in a very controversial manner the strong pressures in the state for oil, gas, timber and other development.

Byrd had no trouble collecting 23 signatures for his cloture petition, and little difficulty is expected obtaining the three-fifths vote needed to shut off debate when the Senate returns Aug. 18.

Discussion then is to proceed on a substitute to the bill that has been worked out in off-the-floor sessions among the major antagonists, other than Gravel, who want some kind of legislation this year. That outcome is not certain, however.

A coalition of 52 environmentalist groups took a long look at the compromise worked out by their champion, Sen. Paul E. Tsongas (D-Mass.), with Sen. Henry M. Jackson (D-Wash.), head of the Energy Committee, and said it was unacceptable as a final product.

Closed-door negotiations have focused for the last 10 days on working out something on which the House and Senate can agree without having to go to a conference committee, which would be subject to a killing filibuster by Gravel.

The 300-page Jackson-tsongas compromise package would add 18 million acres of wilderness to Jackson's original Energy Committee proposal. It would eliminate a five-way division of the Gates of the Arctic area and restore it to a national park, but would keep an access corridor the environmentalists detest. river protection designations and management language the coalition wanted were agreed to, as was wilderness designation for most of Admiralty Island in the Southeast.

However, parts of Admiralty would remain under the less restrictive "Preserve" label, as would the southeast's Misty Fjords, where timber interests say thousands of jobs are at stake.

The coalition members object to that, and also to what they say is their main problem: an oil-gas exploration permit for the caribou calving grounds near the northeast corner of the state in the Arctic National Wildlife Range.

The Energy Committee regards that area as a mini-Kuwait and decided to allow seismic exploration and study of the area. Congress still would have to approve drilling.