“A shutdown has these cascading effects on the scientific work of the organization,” said Daniel M. Ashe, a former director of the Fish and Wildlife Service. “They’re hard to foresee or predict right now, but they’re crippling, really, and they affect the organization not for three or four weeks, but for the rest of the year because of all of this complex orchestration of field work.”

The Fish and Wildlife Service declined to comment beyond its published contingency plan, an eight-page document covering nearly 8,400 employees.

The effects could soon reach beyond government workers and labs, and scientists who are not on Washington’s direct payroll have been fretting over how the shutdown might interrupt the flow of grant money to researchers across the United States. The National Science Foundation, which underwrites billions of dollars in research each year, will cancel dozens of proposal review panel meetings this month if the government remains closed. Other agencies that dole out research money have also effectively put their plans for future spending on hold.

“Having that review process literally shut down now, plus also having the budget year truncated, puts a ton of pressure in terms of getting money out to the states and these federal-state partnerships in order to do science,” said Dr. W. Russell Callender, the director of Washington Sea Grant, which receives money from NOAA and is based at the University of Washington.

“You need the feds as a partner in order to be able to conduct the science the states need,” said Dr. Callender, a former NOAA official, “and to be able to get the money the states need.”

The turmoil also spread elsewhere in higher education. Andrew Dessler, a professor of atmospheric sciences at Texas A&M University, wrote on Twitter on Friday that he would not accept any new graduate students because he had proposals pending with NASA and the National Science Foundation.

“I don’t want to accept a student and then find out I don’t have funding for them,” he wrote.

Stopgap solutions, scientists said, will prove unworkable if the shutdown lasts for “months or even years,” as Senator Chuck Schumer of New York, the Democratic leader, said President Trump threatened on Friday.