WASHINGTON — President Obama plans to nominate the government’s top-ranking civil rights lawyer as the new secretary of Labor on Monday, a key position as the administration prepares to take on immigration reform.

Thomas E. Perez’s nomination had been expected, but the administration said last week that the announcement was not imminent. If confirmed by the Senate, Perez would be the only Latino in Obama’s second-term Cabinet. He is the assistant attorney general for the Justice Department’s Civil Rights Division.

An administration official said Sunday that Obama would name Perez to succeed Hilda L. Solis, a former member of Congress from California who decided to leave the Labor post. The other Latino in the first-term Cabinet, former Sen. Ken Salazar of Colorado, is stepping down as secretary of the Interior. The official spoke on the condition of anonymity because he was not authorized to discuss the nomination before the White House announcement.

Perez, a Harvard-educated lawyer, is a first-generation Dominican American with a long career in public service. Although Democratic supporters consider him a vigorous advocate of worker rights, he could face a challenge from Republicans angry about initiatives at the Justice Department.

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