Navy flag officers and top executives were told Thursday to begin cutting expenses -- laying off thousands of temporary civilian workers, reducing base operations and preparing to cancel maintenance work on more than two dozen ships and hundreds of aircraft.

Adm. Jonathan Greenert, chief of naval operations, directed the reductions in a memorandum sent to senior Navy officials. The cuts are driven by uncertainty over how much a divided Congress and the White House might approve for the Pentagon's 2013 budget.

"We are making the following reductions, starting now, to ensure we can fund ongoing deployments and other mission-critical activities," the memo said.

The reductions do not specifically mention Navy operations in Hampton Roads, but they are expected to affect numerous private and military facilities in the region -- as well as ships and aircraft. Southeast Virginia is home to multiple bases, including the Navy's largest, Norfolk Naval Station, and Norfolk Naval Shipyard, a government-owned facility in Portsmouth where thousands of civilians work on Navy vessels.

The cuts include:

-- Plans to cancel maintenance for about 30 Navy ships at private shipyards between April and September.

-- Plans to cancel depot maintenance for about 250 aircraft between April and September.

-- Terminations of temporary civilian employees and a civilian hiring freeze. This will reduce the shipyards' workforce by more than 3,000 people.

-- Reductions in base spending and plans to cancel most repairs and upgrades of piers, runways, buildings and other facilities.

Private ship-repair operators said last week they were already feeling the effects of the cutbacks, noting that new repair contracts aren't being approved.

"This is a big deal for all those yards here that have been hiring," said Craig Quigley, executive director of the Hampton Roads Military and Federal Facilities Alliance. "They have been investing.... They have been doing advance purchases. This completely pulls the rug out from under them."

Greenert stated that if Congress takes action to provide more money or permits the Navy to shift funds, the cuts could be avoided.

"These reductions are intended to be reversible," said Greenert, who will be in Norfolk today for an all-hands meeting with sailors.

The cutbacks are in response to Congress' continuing to fund the Navy at the 2012 budget level, rather than providing what the service was expecting for 2013. Unable to agree on an annual budget, Congress approved a continuing resolution to keep the government operating at 2012 budget levels until March 27.

Congress will have to decide by then how to fund the remainder of the fiscal year.

The smaller budget and other "unplanned growth" leave the Navy with $4.6 billion less than it needs for 2013, the memo says.

However, even if money is restored later for maintenance and other projects, Greenert indicated, the delays will be costly.

"Much like putting off an oil change because you can't afford the $20 service, we save in the short term, but shorten the car's life and add to the backlog of work for later," he wrote.

The reductions are separate from about $1 trillion in automatic budget cuts -- known as sequestration -- with more than half coming from the military. Those are set to begin March 1, unless Congress intercedes.