On Tuesday, the Assembly becomes the first state legislative body in the nation to be led by a black woman. In Washington State, Rosa Franklin is Senate president pro tem, a largely ceremonial role.

Karen Bass, a former activist from Los Angeles, takes the helm of the Democratic-led Assembly, the first of several legislative leaderships in Sacramento.

The change occurs after the failure by Ms. Bass’s predecessor, Fabian Núñez, and others to alter nearly 20-year-old term limit laws. The issue catapulted Ms. Bass into her powerful role when the state is in a fiscal crisis.

One of her main responsibilities will be to lasso the 80-member body around the discussions over what to do about the $12 billion to $15 billion deficit.

Ms. Bass begins with a track record with Gov. Arnold Schwarzenegger, a Republican, who has called her a terrific leader and with whom she worked on the foster care system.

“He’s a Republican, and I’m a Democrat,” Ms. Bass said in a telephone interview from Sacramento, where she lives half the week. “I would describe it as a positive relationship.”

Leading the Assembly “is not a job I’ve always dreamed of,” said Ms. Bass, who before being elected from the 47th Assembly District in 2005 ran the Community Coalition in South Los Angeles. “I have been a lifelong community activist and frankly did not dream of being in public office.”

Serious-minded — her idea of a good time is to form a commission to study the state’s tax structure — and rather unyielding, with a brown belt in tae kwon do, Ms. Bass was also one of the first high-profile elected officials to support Senator Barack Obama’s candidacy here.

Mr. Núñez was the longest-serving Assembly leader since term limits began 18 years ago.