She still stands proudly in New York harbor, an icon of freedom for nearly 100 years. But the Statue of Liberty is in need of substantial repair.

This is the bad news presented yesterday to the National Park Service by a team of French and American architects and engineers. The good news is that the job, though tricky and costly, can be done by Oct. 28, 1986, the centennial anniversary of the great lady's dedication.

Costs for the repairs could go as high as $30 million, all of it to be raised privately from the "Franco-American business and cultural communities" by the French-American Committee for the Restoration of the Statue of Liberty.

But money seemed last on the list of concerns voiced yesterday by members of the committee as they detailed the damage done to the statue by time itself and nearly a century's exposure to wind, rain and polluted air.

The colossal statue, designed by Alsatian sculptor Auguste Bartholdi and constructed of 300 hammered copper plates connected to an ingenious iron skeleton conceived by structural engineer Gustave Eiffel, was donated by France to the United States "to celebrate . . . the old and sincere friendship which has so long united both nations."

That spirit was revived yesterday by Philippe Valery-Radot, chairman of the committee, who concluded a short, moving address--"the summer of the liberation of France was the best summer of my life"--with a champagne toast to continued friendship between the two countries.

The most severe structural problems discovered after two years of careful study exist in the statue's famous upraised arm and in the torch. The arm was poorly attached in the first place, engineers reported, and the torch has been ruined by corrosion. The arm can perhaps be repaired in place, but the torch will have to be removed and rebuilt.

Among other significant injuries cited in the report is the rusting, both outside and inside, of the statue's thin copper skin. To accomplish needed exterior repairs a giant scaffold will be erected to surround the entire monument--in itself an engineering feat, because, to prevent corrosion to the statue's skin caused by contact with another metal, the scaffold will have to be self-supporting. Construction of the scaffold will begin early this fall.

Engineers also found substantial damage on the inside of the huge structure, although the basic support system--great iron pylons resting on giant iron foundations--needs nothing more than minor repairs. But Eiffel's lacy armature, a vast skeletal structure consisting of 600 vertical ribs and 750 horizontal ribs and designed to accommodate movement caused by wind, no longer performs. It will have to be entirely reconstructed, and repairs will have to be made to correct buckling in the rigid iron framework that supports it. In addition, some 25,000 rivets, shorn by movement, corrosion and chemical deterioration resulting from the contact between iron and copper, will have to be replaced.

Though not originally intended to receive visitors, the monument has been a popular attraction from the day it was dedicated. The rusty, narrow spiral staircase was designed for the use of an occasional maintenance worker, but last year 1.7 million visitors climbed it to see New York (and New Jersey) from a rickety platform underneath the spiked crown.

The statue will be closed for an as yet undetermined length of time during repairs, but when they are completed, visitors should be able to enjoy it more. Architects gave the Park Service four options--from simply fixing up the existing staircase and platform to the installation of new staircases or glass-enclosed elevators--to improve "the quality of the visit."

The most amazing of the engineers' discoveries is that the head of the monument, which Bartholdi is said to have modeled after the head of his mother, actually is two feet off center. Why? Because when the great figure was disassembled in Paris, crated, shipped and then reassembled in New York, things did not go exactly as planned. A discrepancy of an inch or two at the bottom amounted to two feet at the top.

Fortunately, this means nothing in structural or esthetic terms, and the head will remain in place. Richard Hayden, a New York architect who presented the technical study, summed it up: "She looks beautiful the way she is, and we're not going to deal with her cosmetically."