by Katie Zezima, New York Times

Attorney General Martha Coakley Tuesday became the first candidate to begin the formal process for seeking election to the late Edward M. Kennedy’s seat in the United States Senate.

A representative for Ms. Coakley picked up nominating papers from the Secretary of State William F. Galvin’s office Tuesday, said Brian McNiff, a spokesman for Mr. Galvin. Alex Zaroulis, a spokeswoman for Ms. Coakley, confirmed that she had begun taking steps toward a bid for the office.

Ms. Coakley, a Democrat, must now gather 10,000 signatures by Oct. 20 in order to participate in the Dec. 8 primary. The special election for Mr. Kennedy’s seat will be held Jan. 19. Ms. Coakley has not officially announced her candidacy.

Separately, the state Legislature will begin considering another proposal to change state law so that the governor would have the authority to make an interim appointment until the special election is held.

Ms. Coakley, who was overwhelmingly elected attorney general in 2006, has long been considered a possible contender for an open Senate seat.

The Associated Press reported earlier this year that in both 2004 and 2008, Ms. Coakley opened a bank account that financed polling to explore her chances for a Senate seat. She told the Boston Globe in April that the account is inactive but open.

“There may be a [open] Senate seat in 2012 or 2014. It’s just something that I certainly don’t rule out and would be interested in,” Ms. Coakley told the newspaper.

Ms. Coakley told reporters at a news conference about a same-sex marriage lawsuit in July that she planned to seek re-election to her current post.

Jeffrey Berry, a political science professor at Tufts University, said the ambitions of Ms. Coakley, who has risen rapidly from prosecutor to county district attorney to attorney general, are well-known.

“She’s moved up the ladder quite quickly,” Professor Berry said. “She’s had her eye on a Senate seat and has been waiting for the call, and it finally came.”

On Monday, Gov. Deval L. Patrick set the date of the special election, and continued calls to change the law so he can appoint an interim successor. Senator Kennedy suggested the law change in a letter delivered to legislative leaders shortly before his death last week.

Other possible contenders include Joseph P. Kennedy II, Mr. Kennedy’s nephew, Representatives Michael E. Capuano, Steven F. Lynch and Edward J. Markey, and former Representative Martin T. Meehan, who retired in 2007 to become the chancellor at the University of Massachusetts, Lowell. Mr. Kennedy’s widow, Victoria Reggie Kennedy, has said she is not interested in the seat, people close to the family said.