During her one term in the House of Representatives, from a largely rural, traditionally Republican district, Kirsten E. Gillibrand was on safe political ground adopting a tough stance against illegal immigration.

Ms. Gillibrand, a Democrat, opposed any sort of amnesty for illegal immigrants, supported deputizing local law enforcement officers to enforce federal immigration laws, spoke out against Gov. Eliot Spitzer’s proposal to allow illegal immigrants to have driver’s licenses and sought to make English the official language of the United States.

But since her appointment by Gov. David A. Paterson last week to fill the Senate seat vacated by Hillary Rodham Clinton, Ms. Gillibrand has found herself besieged by immigrant advocates and Democratic colleagues who have cast her as out of step with a majority of the state, with its big cities and sprawling immigrant enclaves.

Immediately following the announcement, liberal blogs and New York’s ethnic media lit up with complaints about Ms. Gillibrand’s positions. A group of Hispanic state lawmakers have threatened to support a primary challenger to Ms. Gillibrand, who must stand for election next year. And El Diario La Prensa, the Spanish-language daily, described her as “a disappointing choice.”