Twenty-four years ago, Clement Conger said, he looked at the new State Department Diplomatic Reception Rooms and pronounced them "GSA Low-Bid Modern, Circa '60s."

Since then, Conger has spent $8.13 million, of which $300,000 is yet to be donated. His aim: rebuilding the top-floor diplomatic reception rooms of the State Department in the style of a Philadelphia town house of the Federal Period to provide a setting for a $30 million collection of American antiques. All construction and antiques were paid for with private donations.

Last night it became clear that he's built not a town house but a neoclassic palace.

At a lavish party for 500 donors, Secretary of State George Shultz and Conger, curator at both the State Department and the White House, opened the final sections: the $3.55 million Benjamin Franklin Dining Room and the secretary of state's $1.95 million, 10-room suite.

The great Franklin hall alone is perhaps one of the grandest rooms built in a traditional style in 100 years in North America. The 47-by-102-foot dining room, with a ceiling 21 feet high (raised from 17 feet), is without precedent in Colonial or Federal America. Instead, John Blatteau of Philadelphia, architect for the remodeling, looked to British and French ballrooms and great halls for precedents, especially the hall at Kettleson in Britain, designed by Robert Adam in the late 18th century.

"No expense spared," said an onlooker. "You can say that again," said Conger. "We went over the estimates by $1.5 million. We've exhausted all our contingency funds, we have sold at auction donated antiques given with the understanding they would be sold and we have bills yet to come in."

Shultz announced some help last night -- a pledge of $1.2 million from the J.N. Pew Charitable Trust of Philadelphia, a Sun Oil foundation. Robert Smith, head of the Glenmede Trust, which oversees the Pew foundations, was on hand, pointing out that "Franklin was a Philadelphian, too." Other large donations came from Henry S. McNeil, a former member of the board for the rooms, William Ward Foshay of the Dunley Milbank Foundation, Janet Annenberg Hooker and Mr. and Mrs. David S. Ingalls.

In the dining room, the plaster ceiling decoration, centered by the Great Seal of the United States, and the elaborate entablature, soffit and moldings are ornamented with 30 ounces of 24-carat gold leaf, worth $35,000, applied at a labor cost of $190,000. The huge, fluted Corinthian columns that march down the room are scagliola, concrete cast with red color to look like marble. The six-foot-high fireplace at one end of the room, with Franklin's portrait above it, is dwarfed by the room's sheer size. Six large chandeliers, made of leaded glass in Portugal (at a cost of $275,000 for the set), give glitter to the gold.

Guests last night also took the opportunity to walk through the secretary of state's suite, designed by Allan Greenberg of New Haven, Conn. They saw 10 rooms of elaborate wood carving -- the reception rooms are inspired by Stratford Hall in Virginia. The most elaborate room is the secretary's office, with Corinthian pilasters topped with capitals incorporating the Great Seal of the United States in their design.

In remarks after the lavish buffet, Shultz said of his suite, "I cleaned it up a bit. If you see a paper stamped Top Secret -- it's a joke."

The secretary added he thought his office was quite a change from the way it looked when "Dean Acheson said his office looked like the second-class dining salon on the Europa."

Among those admiring the Franklin room and the offices were Hooker, hailed by Conger as the project's "staunchest supporter," Clare Boothe Luce, now a member of the President's Foreign Intelligence Advisory Board; Selwa Roosevelt, chief of protocol; and Bill Adair, the gilder, who said the gold leaf in the Franklin Room took his crew 5,633 hours.

Shultz shook hands with a contraption on his hand to protect his sore little finger. His wife Helena is hospitalized with a back ailment, a staff aide said.

Both Conger and the secretary put their money where their interest is. Conger and his wife Lianne gave $77,000 from the family trust fund and Shultz and his wife $10,000. In all, the State Department's fine arts committee raised $2.94 million in the last year, a million more than ever before.