FROM THE SIDE it looked like a bashful horse - with bridge beams for its legs and back, and a submarine buoy like a knot in the tail. The lowered head is the bow of the cargo ship SS Westage, long out of Los Angeles. But that was last evening, when the sculptor was still uncertain if he would add the cab of a 1952 diesel locomotive to his work. Touch and go, to the wire.

The sculptor is Mark di Suvero who, for the past week, has judged 35 tons of scrap metal, and erected this massive structure, called Isis, in front of the Hirshhorn Gallery, where it will be dedicated this morning. Isis as "a gift to the American people," and for the next few months the American people cill be calling it either stupid or great.

Whether Isis is stupid or great, history will judge. (History will have plenty of time, since nobody's going to be moving the thing for a while.) Whether or not Isis is a fitting gift to the American people is a tougher question, however. And the answer is probably "yes," for the following reasons:

The sculpture is big: 43 feet tall, 65 feet long, 33 feet wide. In a country where size means impressiveness, Isis is impressive.

The work is made of scrap, a monument to Yankee knowledge know-how. It has also been produced spontaneously, which adds the implication of American exuberance.

The sculpture is the work of an immigrant.

Isis is the gift of an organization built up by immigrants who, in their Annual Report for 1977, celebrate their struggle from scraps to riches "in the tough league of a no-nonsence America."

The sculpture is an ad-a "gift" sincerely given, but an advertisement for the donors as well.

Isis is a gift from private enterprise to a public institution, a symbol of partnership between citizen and state.

Its materials are a tribute to industry, specifically to transportation. The work speaks for speed, size and progress above all.

The question we're left with, then, is: Is Isis art? And the answer to that is probably "no." There's no doubt that the work has integrity; it suits the nation to which it is given. But what it does not have is interior life, the sense that an important idea or feeling called it into being. Enthusiasm called the sculpture into being, but enthusiasm is not enough. Long after this morning of dedication people will be stalking about our gift horse, trying to get the proper perspective on it, but no deeper quest will move them.

There is, of course, one other question that the sculpture raises, and for that alone it is worth a look: In what sort of civilization does a work of sculpture that is not art have integrity? The short answer is: ours.