Spacious, vaulted, softly illuminated stations - with honeycombed walls and seemingly floating mezzanines - have become a hallmark of Washington controversial Metro transit system.

The cavernous, underground stations were elaborately designed under pressure from the U.S. Fine Arts Commission and have drawn considerable praise from government officials, architects and critics.

Yesterday, the future of Metro's longs-standing architectural themes and concepts was thrown into doubt by a newly issued consultants' study.

It suggested scraping existing plans for three Montgomery County Metro stops and replacing them with shallowe, more tube-like or box-like subway stations. The shift was proposed as an economy move, likely to save about $19 million.

The proposal for an architectural revamping was the latest development in a complex and continuing controversy over plans for extending Metro's Red Line from Silver Spring to Glenmont in Montgomery County.

If the architectural shape fo three planned stops on this 4.6-mile segment of the Red Line - those at Forest Glen, Wheaton and Glenmont - were significantly altered, as the consultants proposed, the shift might open the way, officials say, for similar architectural revision at other subway stations that have not yet been built. The recommendations prompted mixed reactions.

Montgomery County Executive James P. Gleason, a key figure in key firuer in the controversy, praised the consultants' proposals, saying he had long been a "lone voice" calling for more modest and less costly stations then those Metro decided to build. "There's a lot of wasted space in them," he said.

Charles H. Atherton, executive secretary of the Fine Arts Commission, expressed some dismay. "I think we'd be disappointed to see any cutting back - any short-cutting of the design," he said. "This is a long-term investment."

Theodore C. Lutz, Metro's general manager, appeared to find himself in a new predicament. "We're sort of caught between some conflicting federal objectives," he said.

On one hand, Lutz noted, Metro was under pressure from Secretary of transportation Brock Adams to trim costs on the Silver Spring-to-Gelnsdont stretch.

On the other hand, Lutz pointd out, Adams had recently pressed for a "new policy" of urging broader use of artistic design in transportation systems. Adams had been joined by Joan Mondale, the Vice President's wife, when he made his announcement in September. He had cited Metro as an example of a "well-designed" transit system.

The architecture of Metro's stations has had a considerable history. In 1966, President Lyndon B. Johnson asked for a "worldwide" search for architectural concepts that would make the planned subway network "among the most attractive in the world." Metro architectural advisers did, indeed, study subway systems in several nations. Much debate ensued before an architectural plan was hammered out.

In 1971, not long after the subway's construction began, Washington Post architectural critic Wolf Von Eckardt praised the stations for their "noble spaciousness" and "serene kind of beauty." He said he had found in the Metro system " a quality of design that is rare in municipal architecture and unheard of in American public transportation since the great railroad stations at the turn of the century."

Metro's architectural planners had decided to use the same overall pattern for every subway station. A single uniform design, officials say, was intended to give a sense of unity to the entire rail system.

The new recommendations by two consulting teams - the engineering firm of DeLeuw, Cather & Co. and the architectural firm of Harry Weese & Associates - hinge on a proposed shift in architectural planning. No decision on whether to follow the consultants' cost-cutting proposals is expected for several weeks.

The federal government had demanded a new study of the Silver Spring-to-Glenmont stretch because it is considered the costliest suburban link in the planned rail system. Of numerous options examined by the consultants, only one was found to be cheaper to build than what Metro had previously planned. The savings gained under the cost-cutting plan, the consultants said, would result almost entirely from changes in the stations' design.

According to the consultants, the Silver Spring-to-Glenmont connection, as currently planned, would cost $372 million. By revamping these plans, Metro could trim its construction costs to $352.6 million, the consultants said.

At the Forest Glen and Wheaton stations, Metro's sweeping arches would be replaced by two, smaller, separated tubes, if the consultants' proposals are followed. The Glenmont station would assume a box-like shape, encumbered by support columns.