A young woman was stabbed numerous times in the lobby of an Upper East Side building where she works — and cops are on the hunt for her ex-boyfriend, sources said.

The unidentified victim, who was expected to survive the bloody attack, is an employee at the The Robert Sterling Clark Foundation at the northwest corner of Lexington Avenue and East 64th Street about 2:30 p.m.

She was treated at the scene for multiple stab wounds to her abdomen and elsewhere and later taken to New York Presbyterian Hospital in serious but stable condition.

Cops were looking for her ex, described as a black male in his 40s wearing a red shirt, who is believed to have fled on foot.

The foundation was launched in 1952 and to support an art collection and arts fellowship at Williams College.

They later expanded their mission to “focus on work in New York City which broadens and deepens knowledge of and participation in the arts across the city’s diverse and culturally rich population,” according to their Web site.

And they also work to safeguard reproductive rights and women’s health, and conduct research to ensure that local and state governments operate effectively.

Clark, an 1899 Yale grad and heir to the Singer Company fortune, lived a life of adventure, fighting in the Spanish American War and with American troops in China’s Boxer Rebellion.

He lived in China, Paris and elsewhere around the world and was married to the famed French actress Francine Clary.

His grandfather, Edward, had graduated from Williams College in 1831, and both his grandfather and his father, Alfred, had served as Trustees, and he donated his collection to create an art institute at the college in Williamstown.

He died in 1955 at the age of 78 but his foundation continued its charitable efforts.