Architectural plans for the United States Holocaust Memorial Museum, unveiled yesterday at a subcommittee hearing on Capitol Hill, show a larger, more assertive building than was envisioned two years ago, when plans for the museum-memorial complex were initially revealed.

The most memorable facet of the building, to be located at midblock between 14th and 15th streets south of Independence Avenue, will be a powerfully sculpted 15th Street facade in which a granite-sheathed, hexagonal Hall of Remembrance, nearly 40 feet high, will hover some 20 feet above the main entrance.

Made possible by contemporary engineering -- the massive hall will be suspended from steel trusses in the superstructure -- this device has great expressive potential. The space underneath the hovering form could become an austere, somber passageway appropriate to a place devoted to the eternal remembrance of the Holocaust. Inside, the hall -- to be designed by national competition -- could become a rich, contemplative chamber appropriate to an institution devoted to assuring "that it will never happen again to any people."

But the design needs tempering and refinement in scale and detail. "This is a very preliminary design," architect George Notter, of the Washington firm Notter, Finegold & Alexander, emphasized at yesterday's hearing of the House Appropriations subcommittee chaired by Rep. Sidney Yates (D-Ill.), where officials of the Holocaust Memorial Council were seeking approval of a $1.95 million operating budget for fiscal 1986. (The $30 million building as well as the institution's approximately $50 million program for exhibits and research will be financed by private contributions.)

Notter said this to his credit, for if the design were built as shown it would be too big, too stark and too aggressive for its sensitive site between two older structures (the picturesque Auditor's Complex to the north and the Classic Revival Bureau of Engraving and Printing to the south) and near the monumental core of the city and nation.

The chief design problem is to create a balance between competing claims of symbolism, urban design and function.

In terms of symbolism, a balance must be achieved between the story of national union so magnificently told from the Grant statue below the Capitol to the Lincoln Memorial at the other end of the Mall, and the tragic tale of the Holocaust represented by the new memorial. This is no easy challenge, and it can only be met if the latter building takes a distinctly secondary position, which, so far, it does not.

The urban design issue is similarly delicate -- it is no easy matter to build a monumental memorial in the middle of a city block between two older buildings, each of a different architectural character. As the design now stands, the Holocaust building would overpower its neighbors.

The functional requirements established by the memorial council are at least partially responsible for this impasse. The building is to be at once a memorial, a museum and a learning center with significant archival holdings for scholars as well as innovative educational programs for lay persons of all ages.

As planned, the building will house an auditorium, a cafeteria and service facilities on a basement level, a grand entrance hallway extending its entire length on the ground floor, three tiers of exhibit space and the memorial hall on its middle level, and two stories for the library and archival storage on the top. Measured from ground level at 15th Street, it will be more than 90 feet high.

As Notter testified yesterday, the approximately 275,000 square feet of space needed to meet these requirements far exceeded the capacity of the two vacant buildings that currently occupy the site -- low, rather nondescript outbuildings of the Auditor's Complex that were constructed early in this century. Hence, he explained, the decision was made last fall to design a new building rather than recondition the old ones, which was the original intention.

There is an irony in this decision in view of the heartfelt responses of many council members who, when they first visited the site, compared these innocuous buildings to those of Nazi concentration camps. But, besides being functionally inadequate, these older buildings were not symbolically appropriate to their new use -- they offered no chance at all for the creation of a space suitable to memorialize the dead of the Holocaust.

Having rendered this judgment, I must admit the irony of my objecting to the new building because of its size. Nonetheless, I do. It is a difficult task to create a building whose form and scale are at once polite and symbolically distinct, and although Notter and his colleagues (Mariani & Associates, associate architects; and Karl Kaufman, consulting architect) have made an excellent beginning with the temple-like structure extending the full 375 feet of the block between 15th and 14th streets, it is just that -- a beginning.

What can be done? The most drastic solution would be to reduce significantly the size of the structure while maintaining its basic form. This could be done only by removing an important element of the council's program to another building. Pressed by a congressional deadline to start construction -- it must begin by October -- the council had to dismiss a promising solution, which was to house certain functions of the institution in an adjacent part of the Auditor's Complex. I can only ask, why the rush? Why eliminate for the sake of an arbitrary deadline the best long-range opportunity to solve simultaneously the problems of the building's overweening size and the institution's functional needs?

If this is not done, there are many ways the size of the project could be reduced and the design improved without tremendously impairing the council's ability to carry out its program. Parking for 150 to 175 cars could be severely cut or eliminated. Floor plans and floor heights, especially that of the rather open 20-foot-high ground floor, could be squeezed in the name of esthetics and economy. The building could be redesigned on its eastern, 14th Street end to accommodate more usable space. The size of the memorial hall could be reduced quite a bit without harming its expressive potential.

Spatial concerns aside, there are numerous design refinements that can be made to reduce the building's assertiveness as well as its apparent bulk.

An important improvement would be to change the color of the building's granite facing from the darkish red of the model presented yesterday to a lighter color that would better harmonize with the neighboring structures. (This is, indeed, being considered, Notter pointed out.) Another would be to force the building back somewhat from 15th Street, the better to align with the long facade and cornice line of the Bureau of Engraving and Printing. Another would be to somehow modulate the stark, post-and-lintel street elevations with subtle changes in color or texture. The open, landscaped forecourts at 15th Street can be enlivened with appropriate ornamental or sculptural groupings.

Not all of these changes are necessary, but some of them are if the building is to live up to its enormous potential. Fortunately, there still is time. The design will be submitted to the Commission of Fine Arts and the Historic Preservation Review Board Wednesday, and to the National Capital Planning Commission on May 30.