Albany, N.Y. ? Instantly opening a rift among New York Democrats, Rep. Kirsten Gillibrand — a little-known, pro-gun Democrat from a rural Republican district — won appointment Friday to the Senate seat left vacant by Hillary Rodham Clinton.

Gov. David Paterson announced his choice a day after presumed front-runner Caroline Kennedy — a woman with considerably more star power but less experience — mysteriously dropped out of contention in an embarrassing turn of events that touched off sniping between the governor and the Kennedy camp.

Gillibrand, at 42, will be the youngest member of the Senate and one of 17 women in the chamber.

The second-term congresswoman will assume the seat once held by Kennedy’s uncle Robert F. Kennedy as well as by Daniel Patrick Moynihan.

“For many in New York state, this is the first time you’ve heard my name and you don’t know much about me,” said Gillibrand (pronounced JILL-ih-brand). “Over the next two years, you will get to know me. And, more importantly, I will get to know you.”

Before the governor even took the podium to introduce Gillibrand, anti-gun crusader Rep. Carolyn McCarthy said she would challenge Gillibrand in the Democratic primary next year, or find someone who would. Gillibrand has a 100 percent voting record with the National Rifle Association.