With the year 2000 and its potential for computer-related problems less than 13 days away, Washington area officials are mobilizing an unprecedented volume of people, equipment and supplies--a buildup that follows months of pretend-it's-New-Year's emergency drills.

No one is really sure whether it's all necessary, but with Y2K, as with politics, perception makes it real. Or real enough.

And so, driven by worst-case paranoia--the notion that computers having trouble reading "2000" could malfunction and wind up affecting electricity, telephone service and the water supply, among other things--officials are rushing to wrap up their preparations in the waning days of 1999.

"We are hoping that this is all going to be a flop," said John Patton, chief deputy sheriff in the tranquil suburb of Loudoun County, whose office has bought gas masks in case deputies need to use tear gas on New Year's weekend to break up crowds angered by Y2K problems. "We're anticipating that we'll all be ridiculed for overkill. But if it does go bad, we'll be able to deal with it."

There are signs of the mobilization in virtually every jurisdiction in the region.

On Thursday, the District is scheduled to roll out its new 37-foot-long mobile command center, which includes six work stations and a conference room for use by police, fire and other emergency officials during Mall events on New Year's weekend--but also if there are Y2K problems. Cost to taxpayers: $350,000.

In a giant warehouse in Northeast Washington, workers are stockpiling more than $1 million worth of bottled water, generators, ready-to-eat meals, cots, blankets and heaters in case the D.C. government has to shelter thousands of residents.

Meanwhile, Anne Arundel County has recruited amateur radio volunteers to take over police and fire communications if the regular system shuts down. And Fairfax County officials have ordered dry ice so the county's health department can store medicine if the power goes out.

Government officials say they don't want to look foolishly unprepared if, by some remote chance, older computers involved in running everything from traffic lights to power plants to banks freeze up when the date changes from 1999 to 2000.

"We're preparing for the worst," said St. Mary's County Sheriff Richard J. Voorhaar, "and expecting nothing to happen."

If the phones go out in Arlington, county employees will sit in cars with mobile radios at 33 locations, waiting for any turmoil. Residents could walk up to the cars to report fires or crime. The District has 125 similar "emergency service sites." Anne Arundel police have set up "anti-looting patrols" around the county.

Already, the federal and local governments have spent hundreds of millions of dollars making computer repairs and have conducted all sorts of drills to try to simulate problems that could arise because of the calendar change. At Andrews Air Force Base alone, more than 40,000 computers and other types of equipment have been certified as Y2K-ready.

"We've been at it for three years now," said Capt. Paul Roberts, commander of the Patuxent River Naval Air Station in St. Mary's County, echoing the feeling of many officials. "We've tested things to death."

Arlington replaced its entire traffic signal system, and the District--which lagged behind other governments in Y2K repairs but says it will be ready--moved the clock ahead to test its 1,500 traffic lights. Howard County has planted posts at more than 30 key intersections so that if the lights go out, police officers carrying stop signs in their patrol cars can hang them on the posts. Montgomery County also has 200 portable stop signs in case signals fail, as they did during last January's ice storm. The District will station people at the city's 150 busiest intersections if the signals aren't working.

In Prince William County, water towers have been checked and their levels documented, in case water has to be rationed. Even though Howard County uses Baltimore's antiquated water system--"You just go turn a few valves and you've got water," said Y2K coordinator Richard V. Biggs Jr.--the county has made plans to ration 10 million gallons of water to residents at nine locations if something goes wrong.

Prince George's County officials replaced the fuel pumps that provide gasoline to county vehicles. Montgomery, Arlington and other jurisdictions have printed two weeks of payroll checks as a precaution.

The fire engines at Baltimore-Washington International Airport will be revved up just before midnight to be ready for any incidents there. Five minutes before midnight, all Metrorail cars will stop at station platforms and then restart a few minutes past midnight on a night when Metro expects as many as 750,000 riders.

"This is just an extra precaution," Metro spokesman Ray Feldmann said. "We want the trains sitting safely in a station when the midnight hour occurs."

The preparations in some jurisdictions also include setting up shelters where people could eat and sleep. The District has 21 such shelters at schools, recreation centers and other facilities. Prince George's would direct residents to the nearest of the county's 47 fire stations. Montgomery has six high schools for use as shelters, if necessary; the detention center kitchens would prepare food if the shelters open.

Millions of dollars in supplies and equipment are being delivered to warehouses throughout the area. A visit to a D.C. warehouse near Catholic University this week found forklift operator Anthony Green unloading a pallet stacked with 500 bottles of water as his boss, Milton Dyer, checked over a list of supplies still to be delivered by New Year's Eve:

Five hundred cases of water, 3,000 blankets, 6,000 ready-to-eat meals, 1,105 cots, 23 generators, 100 heaters and 150 radios.

The District is rounding up a relic of the past--manual typewriters--in case all things electronic stop functioning. Fairfax has lined up portable toilets for its shelters and emergency command center and has bought battery-powered laptop computers for its building code inspectors to record information during emergency inspections.

Legions of additional emergency personnel are being called in to help out, with some jurisdictions starting their stepped-up staffing as soon as Dec. 28 and continuing through Monday, Jan. 3, the first business day of the new year.

Leave has been canceled for many police officers and firefighters, and hundreds of government employees either will be working or "on call." Fairfax has scheduled 1,500 employees for Y2K duty, with 2,000 more on call. The bill for overtime will be more than $100,000 in several jurisdictions.

Calvert County has tripled its number of officers working New Year's Eve. Loudoun will have 50 deputies--instead of the usual 15--on duty each day from Dec. 27 through New Year's and about 80 patrol officers each night, compared with about 20 officers on most nights. St. Mary's is adding a "power shift" of 18 additional officers and the SWAT team on New Year's Eve.

The Washington region's only nuclear power plant, the Baltimore Gas installation at Calvert Cliffs in Southern Maryland, will have 90 workers--triple the normal contingent--on hand at the plant on New Year's Eve from 8 p.m. until 4 a.m. No one there is expecting any problems, however.

Special 24-hour emergency command centers are set up in every jurisdiction, where representatives of major agencies and top government officials will huddle to monitor and respond to any Y2K problems. The rollover from 1999 to 2000 will take place as much as 12 hours earlier in other parts of the world, tipping off authorities here to potential disruptions.

Although area officials are confident they are ready for any problems associated with the date change, they worry about what they can't control: an ice storm hitting the Mall and stranding thousands of people while the power goes out. Panicked people calling 911 for non-emergencies.

"Our biggest fear is that people will overload the 911 number with frivolous calls, or just dial it to see if it still works," said Arlington County spokesman Dick Bridges. "Like everyone in a college dorm flushing toilets at the same time, it would overload the system."

Prince William's deputy coordinator of emergency services, Tom Hajduk, said he is more concerned about people overreacting to routine problems that have nothing to do with Y2K.

"There are a lot of people out there who think the world's going to come to an end because it's the millennium," Hajduk said. "How they're going to react and what they might do is a big concern."

Part of the uncertainty stems from the mixed messages the public is receiving from government and industry officials: Don't worry about your money, but take out some extra cash. The water supply is safe, but buy bottled water.

"I don't expect trouble, but we have to plan for trouble," replied Peter LaPorte, the District's emergency preparedness director.

James Heller, director of fire and rescue services in Howard, said that "our confidence level is pretty high that the basic infrastructure is going to be there. But by the same token, we want to be sure that if something happens, we're going to be up and ready to deal with it. We won't be out partying."

Staff writers Maria Glod, Annie Gowen, Ann O'Hanlon, Lyndsey Layton, Angela Paik, Lisa Rein, Michael D. Shear, Jackie Spinner, Steve Vogel and Scott Wilson contributed to this report.

CAPTION: Samuel Booth transports bottled water into a warehouse storage area for the D.C. emergency preparedness effort in the event of Y2K problems.