They haven't erupted yet, but White House budget officials are emitting uneasy vibrations about legislation rumbling through Congress to create a national monument to the Mount St. Helens volcano in the state of Washington.

The tremors at the Office of Management and Budget come from provisions that would allow the Weyerhaeuser timber company and the Burlington Northern railroad to trade volcano-damaged lands for unspoiled public forest tracts nearby.

"It's going to cost a lot of dough and we can't justify it," an OMB official said. "We think the tracks of the BN, Weyerhaeuser and Pennzoil are all over this, but they're hiding behind the screen of the tree-huggers."

OMB estimates that inclusion of the private lands in the monument area, along with loss of potential income from the federally owned timber tracts that would be traded, could push the cost of the project to around $300 million.

Congressional committees that developed the legislation maintain the cost would be far less, roughly $300,000 for each of the next three years. And, they argue, it would create a major new attraction for scientists and visitors intrigued by the fallout from the May, 1980, volcanic eruption.

The volcano monument legislation has passed both the House and Senate and conferees are scheduled to meet, possibly this week, to work out minor differences and clear the way for a final bill to be sent to the White House.

The House-passed bill sets aside 115,000 acres for scientific study and recreation around Mount St. Helens, whose eruption left at least 62 persons dead or missing and caused millions of dollars in damage. The Senate version, passed last week, tickets 105,000 acres for the monument.

Although the two bills go well beyond what the administration originally termed acceptable, they fall short of environmentalist proposals that 200,000 acres be included in the protected study-recreation zone.

But once a bill reaches the White House, it faces an uncertain fate. The Reagan administration originally supported an 85,000-acre tract, to be managed by the U.S. Forest Service, as the most palatable "compromise" from an economic standpoint.

OMB's objections, not yet formally transmitted to Congress, have to do with the cost: the loss of potential timber income from public land that the Forest Service would give the companies in return for land within the park.

The land trades, all in or near the Gifford Pinchot National Forest, involve about 17,000 acres of Weyerhaeuser land in the monument zone in return for 4,756 acres of public land. The railroad would give up 16,334 acres to get 2,630 acres of Forest Service property.

Spokesmen for the two firms took issue with OMB suggestions that they will gain undue advantage from the land-and-timber trade. They said that such trades with the Forest Service have been common in the past as a way for each side to consolidate its otherwise checkerboarded holdings.

A Weyerhaeuser official here said, "I have difficulty seeing how we could benefit. The CBO Congressional Budget Office report on this legislation says that in all probability the administration would have incurred about the same costs with its monument plan . . . . We have always approached this as a value-for-value exchange."

Although the Burlington Northern harvested much of its damaged timber after the Mount St. Helens eruptions, leaving the land generally barren, Weyerhaeuser has not attempted to remove fallen or blitzed trees from the tract that would be in the monument area.

OMB is calculating additional potential loss from about 100 mineral claims held by a copper mining affiliate of Pennzoil, the petroleum firm. The legislation, however, excluded the tracts from the monument area.

Rep. James Weaver (D-Ore.), who pushed the bill through his House forestry subcommittee, indicated he was not much concerned with the seismic ripples from the administration. "I've never thought of this as a bailout for those companies," he said. "The monument is a very popular idea in that region and the Washington congressional delegation fully supports it. I assume we would override any presidential veto, if it came to that."