Sen. Patrick J. Leahy of Vermont will remain chairman of the Senate Judiciary Committee rather than asserting his seniority on the Appropriations Committee.

“Chairing the Judiciary Committee and maintaining my seniority on the Appropriations Committee will allow me to protect both the Constitution and Vermont,” Leahy said in a short statement confirming his decision Wednesday.

Leahy had been expected to take over the Appropriations chairmanship, which was left vacant when Sen. Daniel K. Inouye of Hawaii died Monday. Leahy is the most senior Democrat on the panel, and Democrats generally defer to seniority in choosing committee chairmen.

The Vermont Democrat’s decision to remain at Judiciary means Sen. Dianne Feinstein, D-Calif., is likely to remain the head of the Intelligence Committee. She was expected to take over the Judiciary Committee from Leahy.

On Tuesday, Feinstein told reporters that she would not continue as Intelligence chairwoman, implying that she would take the gavel that Leahy would leave behind.

Leahy’s decision means he will be at the forefront of two major legislative policy debates that are expected in 2013: gun control and immigration law changes.

Feinstein, however, will undoubtedly continue to play a big part in the gun control debate as a rank-and-file member of the committee. After the Dec. 14 massacre of 20 children and six adults at Sandy Hook Elementary School in Newtown, Conn., Feinstein renewed her longtime push for a ban on assault weapons and high-capacity magazines.

Sen. Tom Harkin, D-Iowa, is next most senior on the Appropriations panel, but he also has decided to take a pass on the chairmanship. Instead, he will remain atop the Senate Health, Education, Labor and Pensions Committee.

The new chairman of the Appropriations Committee will be Sen. Barbara A. Mikulski, D-Md. Leahy and other lawmakers tweeted their congratulations to her Wednesday afternoon.

“It’s an honor and a privilege to be expected to follow the great leadership of Senator Inouye, one of my most treasured mentors, and become the chairwoman of the Senate Appropriations Committee,” Mikulski said in a statement Wednesday. “It is especially gratifying to be the first woman to lead this powerful committee. I am grateful for this opportunity to fight for the day to day needs of the American people and the long range needs of the nation.”

The Senate Democratic Conference is expected to ratify the changes at its regular Thursday caucus meeting, Mikulski’s office noted.