Rep. Jane Harman (D-Calif) is expected to announce Tuesday she is resigning from Congress.

Harman is expected to step down to succeed former Rep. Lee Hamilton (D-Ind.) as president and CEO of the Woodrow Wilson Center for International Scholars.

A source close to Harman noted, though, that the deal is not yet finalized. The Wilson Center's board will vote on the matter Tuesday.   

Harman sent a letter on Monday to constituents, describing her discussions with the Wilson Center and calling it an "excruciating decision."

"This is an excruciating decision because the distinction of representing the smartest constituents on earth will never be surpassed — nor will my relationships with my exceptional staff and colleagues in Congress," she wrote. "But shaping and leading the Wilson Center is a thrilling new challenge.

"Should this opportunity come to pass, I would be required to resign my seat," she continued. "But please know that I would remain in Congress for some weeks and do everything possible to ensure an orderly transition to whomever is elected to succeed me."

Harman, a member of the Blue Dog coalition, previously served as the ranking member of the House Intelligence Committee before 2006, when Democrats retook control of the House. She was passed over for the top spot by then-Speaker Nancy Pelosi (D-Calif.).

Harman is serving her ninth term. She is the wife of Sidney Harman, the owner of Newsweek, which recently merged with The Daily Beast. 

According to the blog FireDogLake, possible successors to Harman include Los Angeles City Councilwoman Janice Hahn, state Controller John Chiang and California Secretary of State Debra Bowen.

—This post was last updated at 12:35 p.m.