Del. Susan C. Lee (D-Montgomery) takes a photo during the first day of the legislative session Jan. 13, 2010, in Annapolis.(Gail Burton/AP) (Gail Burton/AP)

Del. Susan C. Lee (D-Montgomery) announced Tuesday that she would seek the state Senate seat being vacated next year by Sen. Brian E. Frosh (D-Montgomery) as he runs for attorney general.

Lee, a member of the House since 2002, pledged in a statement that she would continue to be “a strong and effective advocate” for residents of District 16, which she shares with Frosh and two other delegates.

“I want to ensure that we move forward as the leader in education, affordable college, clean environment, quality health care, public safety, transportation and emerging technologies and jobs that will sustain us for the future,” Lee said.

Lee, who had signaled her intentions some time ago, became the first to file for Frosh’s seat in the wake of his entry into a potentially crowded Democratic primary field for attorney general.

Last month, Del. Jon S. Cardin (D-Baltimore County) formally kicked off his campaign for attorney general with a Web video. Others eyeing next June’s primary include Del. C. William Frick (D-Montgomery) and Del. Aisha N. Braveboy (D-Prince George’s).

Lee, a civil rights and intellectual property lawyer, is deputy majority whip in the House. Her legislative focus has included issues affecting women and children, as well as cybersecurity and identity theft.

Her statement included testimonials from Sen. Jamie B. Raskin (D-Montgomery) and Montgomery County State’s Attorney John McCarthy (D), among others.