"Chairing the Judiciary Committee and maintaining my seniority on the Appropriations Committee will allow me to protect both the Constitution and Vermont," the Vermont Democrat said in a one-sentence statement posted on his official website.
It had been expected Leahy would give up his judiciary leadership position to head up the appropriations panel following the death of Sen. Daniel Inouye, D-Hawaii, who had been chairman.
Feinstein, D-Calif., is now likely remain chairwoman of the Intelligence Committee, Roll Call reported.
Sen. Barbara Mikulski, D-Md., is now likely to become the chairwoman of the Appropriations Committee, Roll Call said, with Leahy having tweeted his congratulations to her Wednesday afternoon.
Sen. Tom Harkin, D-Iowa, chairman of the Senate Health Education Labor and Pensions Committee, is likely to remain, despite his outranking Mikulski on the appropriations panel.
Immigration reform and gun control are likely will be the two top issues before the Judiciary Committee in the coming year, The Hill said Wednesday.
The National Journal ranked Feinstein as more conservative than Leahy. She has sided with Republicans on big issues, including the Iraq war in 2002. However, Feinstein has sided with liberals on U.S. Supreme Court appointments.
But Senate Democratic aides say the biggest difference between Leahy and Feinstein is their opinions on gun control, a high-profile issue on the administration agenda in the wake of Friday's massacre in Newtown, Conn., and earlier assaults this year, including the Aurora, Colo., theater shooting.
Feinstein recently said she would introduce legislation to reinstate the federal assault-weapons ban. Leahy has a mixed record on gun control.