NEW YORK.- UBS PaineWebber has promised the Museum of Modern Art 37 works from its vast collection of postwar art, which includes seminal paintings, drawings and sculpture by masters like Andy Warhol, Roy Lichtenstein, Lucian Freud and Jasper Johns. The gift will be the subject of an exhibition in 2005, when the museum’s building in midtown Manhattan reopens after a major expansion. The corporate collection has been assembled over 30 years by Donald B. Marron, chairman of UBS America. Marron, an advocate of art in the workplace, and several in-house curators have compiled a formidable contemporary collection that lines the walls of UBS PaineWebber’s reception areas and conference rooms, offices and hallways nationwide. At last count, the company, formed in 2000 when PaineWebber was sold to the Swiss bank UBS, owned about 850 works by artists including Brice Marden, Chuck Close, Anselm Kiefer and Claes Oldenburg. Many works have been lent to museum exhibitions, and some have become the subjects of their own shows, traveling to places such as Houston, Detroit, San Diego and Boston. Now, after years of being wooed by the museum, the corporation has decided to donate the 37 works, along with seven others that PaineWebber promised MOMA 10 years ago.