From left, Raj Ahuja, John Burgee and Philip Johnson in 1987.

A huge and previously unknown trove of archival material from Philip Johnson’s architectural practice — including his hand-drawn sketches for towers that helped define postmodern architecture — is to be put up for sale by one of Johnson’s former partners, who has had them in storage for years.

The cache contains more than 25,000 design sketches, working drawings, renderings and photographs from the second half of Johnson’s architectural career, covering more than 120 projects from 1968 to 1992. While there are collections of his early work at the Museum of Modern Art, the Getty Museum and the Avery Architectural & Fine Arts Library at Columbia University, documentation from this later period, in which he became known for his tall buildings, is much rarer. Included in the archive is material on the AT&T Building in Manhattan (now Sony’s American headquarters); the Crystal Cathedral in Garden Grove, Calif.; PPG Place in Pittsburgh; Pennzoil Place in Houston; and smaller-scale structures that Johnson built around his celebrated Glass House of 1949 on his property in New Canaan, Conn., now owned by the National Trust for Historic Preservation.

That period was “the pinnacle of Johnson’s career” as an architect, said Willis Van Devanter, an appraiser of architectural materials hired to examine the archive by lawyers for the archive’s owner, Raj Ahuja. Mr. Van Devanter described the archive as “absolutely essential to the study of modern architecture,” given Johnson’s stature as “the major influence in world architecture of the latter 20th century.”

Still, that stature was arguably based more on his role as a leading advocate for Modernism and subsequent architectural movements — beginning with the International Style show he helped organize at the Museum of Modern Art in 1932 — than on his own design work. Aside from a few of his almost universally praised projects, Johnson has been regarded by some critics and fellow architects as dilettantish, more slave to fashion than serious practitioner.

He was criticized in particular for focusing on aesthetics at the expense of more fundamental issues of function. But Michael Robinson, an expert on 20th-century documents and another appraiser of the archive, said its drawings would do much to help counter that notion.

Mr. Robinson was especially struck, he said, by the degree to which the drawings concern themselves with the surrounding context.

“Nobody thinks of Johnson as a planner,” Mr. Robinson said. “They think of him as an antiurbanist. He really was concerned with how life interacted with these buildings. You get elaborate plans for walkways, roads, the works.”

Calling the archive “extraordinarily complete,” he added, “You literally see him thinking on paper all the way through to the final drawings necessary to actually build a building.”

The archive also offers insight into aesthetic matters, like the evolution of Johnson’s approach to shaping buildings, said Christy MacLear, who until recently was executive director of the Philip Johnson Glass House. For example, she said, the drawings demonstrated similarities in the massing of several notable but modest buildings on the Glass House property and of the vast Crystal Cathedral that Johnson worked on around the same time.

And there are also working drawings for at least 50 unbuilt projects, including London Bridge City, an office complex on the Thames; four Times Square office towers; and a house for Johnson’s companion, David Whitney. The archive “has a lot of things Johnson thought about but never got off the drawing board,” said Wilbert R. Hasbrouck, who was also consulted on the collection and was an owner of the Prairie Avenue Bookshop in Chicago, which has gone out of business. “This archive is going to open up a whole new field of study about his work, particularly on the unbuilt buildings. It fills out a lot of gaps that we didn’t even know existed.”

Mr. Ahuja, the archive’s owner, was a former design partner of Johnson’s. An Indian-born architect, he joined the firm as a young man in 1971 and ran its Iranian office before becoming a partner with Johnson and John Burgee in 1984. During his tenure Mr. Ahuja developed a strong affinity for Johnson, who left the partnership for a consulting role in 1986 and left the practice entirely five years later.

Mr. Ahuja and Mr. Burgee clashed over Johnson’s level of involvement. “I was more for keeping Johnson in the firm as a consultant and as a designer, and Burgee was more determined to get Philip out,” Mr. Ahuja said in an interview. “I thought, without Philip Johnson, we would not be getting the assignments we were getting. He was the man.” (Speaking by telephone from California, where he has retired, Mr. Burgee said he had not forced Johnson out, adding, “He voluntarily withdrew.”)

Mr. Ahuja, now 69, said he ended up with the archival material in 1995 as part of a Chapter 11 proceeding in which Mr. Burgee sought bankruptcy protection for the firm and for himself. The bankruptcy followed an arbitration between Mr. Ahuja and Mr. Burgee in 1988, when Mr. Ahuja left the firm.

Since then, Mr. Ahuja said, he has kept the archive in a warehouse: “The court awarded me the drawings, which I have safeguarded because they are our legacy.” But having paid for its maintenance for years, he added, “it is time to transfer it to respectful hands, and I have my family’s security to think of as well.”

Mr. Ahuja said that he did not know when or how the rest of the collection would be sold. (It has received two separate appraisals, but lawyers for Mr. Ahuja, James Frankel and Andrew Ross of Arent Fox in Manhattan, declined to disclose the valuations.)

Mr. Burgee played down the importance of the archive. “It’s mostly working drawings and drafting drawings,” he said. “We purposely didn’t keep design sketches because they weren’t good enough. Philip was sensitive that he didn’t want his hand drawings shown anywhere.”

Ms. MacLear said that Johnson was known for weak drawing skills. He had a “high-concept” sketching style, she said.

But Mr. Ahuja said standard office procedure had been to roll and store all drawings, and that there had been no policy of destroying Johnson’s.

So far one significant piece of the collection has been sold, in what Mr. Ahuja’s lawyers described as a kind of market test: a seven-and-a-half-foot-tall presentation drawing of the AT&T skyscraper’s facade at 550 Madison Avenue, which the Victoria and Albert Museum of London acquired at auction for $70,000 in April.

However the rest of the archive is sold, Mr. Ahuja said, he hopes it will be bought en masse by a single institution so that it will be available to scholars and students. The architect Robert A. M. Stern, dean of the Yale School of Architecture, said he was sorry that even the single rendering had been sold separately. Although he has not seen the materials, he said, it was clear to him that “the worst thing would be breaking the archive up.”