ANCHORAGE, Alaska » A quietly profound generational change is about to sweep through federal agencies here in the nation’s biggest and wildest state — but also by many measures, its most government-dependent — where hundreds of millions of acres of public land are set aside for national parks and preserves.

The change is being driven by new rules in the federal retirement system that Congress started to phase in during 2009 and, by dint of various schedules and formulas, are hitting home between now and Jan 1. The new rules are focused specifically on equalizing retirement benefits among workers in Alaska, Hawaii, U.S. territories and the lower 48 states.

At the Bureau of Land Management, which oversees the 23-million-acre National Petroleum Reserve, among other vast properties, close to 8 percent of senior staff members will retire early, while more than 7 percent of National Park Service employees have so far said they will do the same.

At the federal Fish and Wildlife Service, which manages 16 wildlife refuges that are collectively about twice the size of Michigan, about one in 11 workers — mostly senior managers, including top officials at five of the refuges — will clock out for the last time on or before Dec. 31.

"It’s unprecedented," said Mitch Ellis, the service’s assistant regional director in charge of Alaskan refuges. "We’ve never had to fill that many manager positions at once before."

The turnover comes at a time of intense focus and pressure for agencies like the Fish and Wildlife Service, which is being hit by both the 2009 congressional act in retirement accounting and an agency-specific package this year that allows early retirements. Years of frozen budgets that started during the recession have already reduced staff and operations. The changes also come against a backdrop of sometimes heated discussion over the service’s shifting mission — how to protect wildlife as giant debates about climate change and energy exploration grip the Arctic.

The agency’s law enforcement arm, which deals with illegal animal harvests and the protection of endangered species, will have relatively few departures, officials said. But often, they said, real protection comes down to education and personal relationships in villages in remote areas — and those conversations, because of new leadership at the refuges, will change.

"This is not a good thing for us," said David C. Raskin, a former president of the Friends of Alaska National Wildlife Refuges, a group that works with and supports the agency’s work. "We have contacts. We know who to call."

In terms of pure head count, the numbers could look trivial. About 55 or so mostly senior managers, scientists and wildlife experts out of a work force of 600 at the Fish and Wildlife Service, spread across Alaska’s vast terrain, have indicated that they will take the retirement package. At the National Park Service, 36 of about 500 employees have said they plan to leave — though the number could change as people reconsider before the end of the year. The driving force pushing people out is that if they stay into next year, they will have to work a year or more to get the full retirement benefits under the new law.

If talks in Washington fail to avert the automatic tax increases and spending cuts scheduled to take effect on Jan. 1 — the so-called fiscal cliff, or sequestration — the effect of the retirements would be compounded, Fish and Wildlife Service officials said, by the question of what positions could then be refilled at all.

"With sequestration, there’s an 8 percent reduction," said Doug Alcorn, an assistant regional director who is among the retirees. "Managers would have to prioritize."

But the impact is not just in the number of people who are going.

At the Fish and Wildlife Service, for example, retirees will take with them more than 1,000 years of cumulative institutional wisdom and conservation experience. At the U.S. Forest Service’s Recreation, Lands and Minerals Office, for example, four top leaders, including the senior minerals geologist, are departing.

And many of these people were shaped by a perspective formed in a very different time in Alaska and the nation — mostly the 1970s, when the environmental movement was young and bursting with muscular and sometimes hippie-tinged enthusiasm.

Alaska, back then, was a magnet for wildlife biologists and seekers of a life at the frontier. The bush was "back to the land" at its most extreme — a force fueled by what one retiring refuge supervisor, Mike Boylan, called "the John Denver effect."

"Everybody coming out of college wanted to go to the woods, into the wild," Boylan said. "Alaska was the big one, if you could get up here."

Alaska is also different than the other areas affected by the federal retirement rule changes in that the federal role here is pervasive and overwhelming. About 226 million acres, almost the size of Texas and Wyoming combined, is federal property in Alaska.

"Alaska was almost written in my destiny," said Bill Larned, 64, a biologist and pilot who started at the Fish and Wildlife Service in 1976 after working as a pack outfitter in Wyoming.

Environmental groups and agency officials also say the retirement wave is momentous in what happens next: new blood coming in at a time when some elements of the old Alaska — doughty homesteaders, trappers and subsistence hunters — are fading. And while environmental groups like the Sierra Club might have once focused on endangered species, climate change — hitting the Arctic with significant effect — is now the focus and the pressure point in dealing with federal land agencies.

"We’re making sure that we’re protecting the land and animals that are part of the Arctic," said Lindsey Hajduk, an Arctic organizer at the Anchorage Sierra Club office. "But it’s in the larger context of climate change."

Some critics of the federal government’s role in Alaska — a tension that dates back to territorial days — said they hoped new blood would be an improvement.

"The loss of knowledge is going to be hard," said Doug Vincent-Lang, the acting director at the wildlife conservation division of the Alaska Department of Fish and Game. But Vincent-Lang said he thought the Fish and Wildlife Service had "fallen away" from its traditional mission of wildlife counts, which were long part of Alaska’s culture of hunting.

"Maybe they’ll come back to it," he said.

Some retiring workers said that as technology has become more and more a tool of landscape study and protection, younger, more tech-savvy leadership might also be good for the wild lands.

"The younger people coming up have such a better handle on how new forms of technology can be used in conservation," said Paul Liedberg, 59, the manager at Togiak National Wildlife Refuge in southwest Alaska, who plans to retire after 36 years. "I cannot even imagine it the way they can."