Mr. Rangel’s use of the fourth apartment as an office, in addition to his 2,500-square-foot residence, was especially troubling to some advocates, given the city’s chronic shortage of housing for low- and moderate-income residents.

“Whether it’s an elected official or not, no one should have four apartments, especially when one is being used as an office,” said Michael McKee, treasurer of the Tenants Political Action Committee, who was not aware of Mr. Rangel’s situation when he was interviewed.

Mr. Rangel, who was first elected to Congress in 1970 and is one of the city’s most recognizable elected officials, has written and spoken extensively about his devotion to his home in Harlem, but does not appear to have ever publicly acknowledged that he has been permitted to lease four rent-stabilized apartments there. According to a public records database and interviews with neighbors, he has lived in the building since the early 1970s, but it is not clear when he amassed the four units.

Mr. Rangel, 78, declined to answer questions during a telephone interview, saying that his housing was a private matter that did not affect his representation of his constituents.

“Why should I help you embarrass me?” he said, before abruptly hanging up.

Olnick officials declined to discuss when or why they decided to permit Mr. Rangel to lease multiple rent-stabilized units. Asked why he had been allowed to use one as an office, Jeanette Bocchino, a spokeswoman for the company, replied: “This is a private matter for the Olnick Organization and Mr. Rangel to evaluate.”

Mr. Rangel is not the only prominent resident with a rent-stabilized apartment at Lenox Terrace. Gov. David A. Paterson told The New York Sun in May that he pays $1,250 for a rent-stabilized two-bedroom apartment in the complex that rents for $2,600 or more at market rates. Basil A. Paterson, the governor’s father, pays $868 per month for his apartment there, in the same building as Mr. Rangel’s apartments, according to state records.