The National Weather Service is preparing for the probability that fewer forecast updates will be fine-tuned by specialists, among other cutbacks, because of “severe shortages” of meteorologists and other employees, according to an internal agency document.

An agreement signed on April 10 between the service and the union representing its employees describes several measures that forecasting offices will take to manage the consequences of the Trump administration’s drive to reduce the size of the government. The document also says the service might reduce or suspend the launches of data-gathering weather balloons and eliminate the testing of new forecasting methods and technologies.

More than 500 people this year have already left the National Oceanic and Atmospheric Administration, which oversees the National Weather Service. Nearly 200 of those departures were people who work in weather forecasting offices, which had already faced serious understaffing.

About 300 additional people are expected to leave under the Trump administration’s latest resignation offer, according to two people familiar with the matter, who asked for anonymity because the administration has not officially made agency departure numbers public. Union officials said the departures at NOAA since President Trump took office have far exceeded the typical turnover rate.

The agreement indicates that field offices across the country could face vacancy rates as high as 35 percent, compared with current staffing levels, according to the union. Parts of the agency had already been operating at lower-than-usual staffing levels well before the Trump administration’s cost-cutting efforts.

The document outlines options for cutting back programs and allows the National Weather Service to offer “degraded” services as more meteorologists retire or resign. The cuts would significantly scale back the work of the 122 weather offices nationwide, which collect weather observations and issue warnings during severe weather events.

Representative Zoe Lofgren, the senior Democrat on the House Committee on Science, Space and Technology, which oversees the Weather Service, said the Trump administration was endangering the agency’s lifesaving work. Democrats on the committee provided a copy of the document to The New York Times.

“Chaotic and illegal firings, coercions to resign, reductions in force, and a general obsession with destroying the morale of dedicated public servants have left the National Weather Service’s work force so strained they cannot carry out their duties as they once did,” Ms. Lofgren said in a statement. Tom Fahy, the legislative counsel for the union, the National Weather Service Employees Organization, said the agreement had been developed to alleviate staff burnout. “In the last four months our losses are unprecedented, and our offices are struggling to maintain operations,” he said.