Washington ? As night falls on inauguration eve, a government slumber party of historic dimensions will begin. Nearly 6,000 soldiers will unroll their sleeping bags in D.C. schools. Homeland Security employees will climb onto bunk beds in trailers. FBI agents will stretch out on cots in a church hall here.

And at the National Museum of American History, a few employees will live the ultimate childhood fantasy: a sleepover in a building with 5,000 musical instruments and a 1,354-piece doll’s house.

With hotel rates sky-high and major bridges and streets closed, many government employees have concluded there is only one sure way to get to their workplaces Tuesday: sleep there. Even officials with decades of experience in Washington said they can’t recall anything similar.

“This is a unique one for all of us,” said Senate Sergeant-at-Arms Terrance W. Gainer, who has rented hundreds of cots for congressional employees.

Tuesday is a holiday for most federal and local government employees. But thousands have to provide security for the expected record crowds, run the inauguration ceremony and carry out other government functions.

They are joining numerous private-sector employees who will also bed down at their workplaces: hotel workers, hairdressers, nurses, chefs, nursing-home employees.

“Many people are going to be shacking up, shall we say,” said Lynne Breaux, president of the Restaurant Association of Metropolitan Washington. She has been here for other inaugurations. But this one, she said, is “once-in-a-millennium.”

Chris Geldart, head of the D.C. regional office at the Department of Homeland Security, scrambled to find hotel rooms for his workers who might not be able to drive or squeeze on to Metro trains. But he couldn’t accommodate them all.

“Cost. That was the issue,” he said.

His solution: trailers. “Not FEMA trailers,” he hastened to add. The vehicles are heated bus-like vehicles typically used at disaster sites.

More than 23,000 law enforcement officers and military personnel will be providing security. Hundreds of police officers will catch some shut-eye on cots at D.C. police stations and at the police academy.

For National Guard troops, floors and sleeping bags will be nothing new. But many will have to contend with pint-sized furniture and urinals.

About 5,900 soldiers were to begin moving into 12 schools here beginning this weekend, military officials said. A thousand more will camp out in tents on the lawn north of the Lincoln Memorial. Three hundred will bunk down at RFK Stadium or the Department of Health and Human Services.

While some well-to-do visitors will be enjoying 400-count Egyptian sheets and champagne at fine hotels, conditions will be fairly spartan for most overnighters.

“I’ve heard talk of those blow-up mattresses,” said Valeska Hilbig, whose American history museum will open early on Inauguration Day, at 8 a.m. She firmly denied that employees would take advantage of the exhibits at night, whipping up something in Julia Child’s kitchen or taking a spin on Evel Knievel’s Harley-Davidson.

“It won’t quite be ‘Night at the Museum,’ ” Hilbig said. Employees will have to snooze in their offices.