WASHINGTON — Seven months into Senator Barbara A. Mikulski’s new assignment as chairwoman of the Senate Appropriations Committee, there is already a saying among members: “We loved Byrd, we respected Inouye, we fear Barbara.”

It is not hard to see why. Ms. Mikulski, a Maryland Democrat, intimidates people in a way that the two most recent committee chairmen, the late Senators Robert C. Byrd of West Virginia and Daniel K. Inouye of Hawaii, did not. During a March floor debate, Ms. Mikulski ordered Senator John McCain of Arizona to go back to his office and read a bill so he could properly vote on it — and Mr. McCain, chastened but cheerful, agreed.

“I will now try to carry out my mission as assigned by the distinguished chairwoman,” he said.

Ms. Mikulski, who legislates with two parts accommodation and one part coercion, now finds herself at the center of a spending brawl on Capitol Hill. At 77, she is the longest serving woman in Congress, the first female leader of its most august committee and the fulcrum in a fiscal fight that will dominate Washington this fall.

With Ms. Mikulski at the helm, the Senate Appropriations Committee — for decades a quiet outpost of bipartisan check-writing financing every corner of the government — is charged with heading off what could be the first shutdown of Washington after three years of near misses. She has already begun by reviving the committee from an earlier somnolence, when staff members directed much of the action and partisan peace was kept by awarding senators money for the pet spending projects universally denounced as earmarks.