Marine Corps Marathon organizers have launched an unprecedented security effort in preparation for Sunday's 26.2-mile race, even holding a military-style drill in which approximately 80 law enforcement and security personnel from 10 organizations discussed potential race-day scenarios, including a bomb threat, a chemical attack and a natural disaster.

Race organizers and local, state and federal law enforcement officials stress that they have received no specific threats concerning Sunday's race and that they don't want to alarm runners or spectators. But several factors convinced organizers to increase security preparations, which had already been significantly bolstered after the terrorist attacks of Sept. 11, 2001, race director Rick Nealis said.

He said these included the timing of the race, which falls two days before the presidential election; the Marine Corps' continued prominence in Iraq; the assault on the lead runner during this summer's Olympic marathon in Athens; and the fact that the race falls on Halloween for the first time in its 29-year history. The marathon course will take more than 22,000 registered runners past virtually all of the Washington area's most notable landmarks, including the Capitol, the Pentagon, and the Washington Monument and Lincoln Memorial.

Race organizers said about 55,000 spectators are expected in the start-finish area near the Iwo Jima Marine Corps War Memorial on Sunday; the race has drawn an estimated 250,000 spectators along the marathon route in the past.

Two weeks ago the Department of Homeland Security sent an information bulletin to organizers of the marathon and of last week's Army Ten-Miler -- which started and finished near the Pentagon -- to describe the current threat level and offer guidance.

"Obviously we're in the nation's capital and we have the icon of the Marine Corps that everyone in the world knows," Nealis said. That has led to "more focus on safety and security -- more than last year, more than [after] 9/11."

Race organizers and law enforcement officials said the race will feature several noticeable security changes. For the first time, there will be five screening points around the entrance to Zone 6, race organizers' term for the area that encompasses the start and finish lines. Marines and law enforcement officers will examine runners' bags at the checkpoints, and organizers are strongly discouraging spectators from bringing bags, coolers or glass containers to the start or finish areas.

The security briefing that was sent to registered runners said there would also be screeners at the pre-race Expo, which begins Thursday at the Hyatt Regency in Crystal City. Nealis said the Expo screening likely will consist primarily of observation by Marines and civilian law enforcement.

Shuttle buses from the race's parking area in Crystal City will be open only to runners with bib numbers until 9 a.m. on Sunday -- another new measure, organizers said -- and participants have been told to arrive two hours early for the race.

Because of changes to the course, the portion of Memorial Drive that passes over Route 110 will be closed to spectators during the beginning of the race.

Dozens of jersey barriers will be brought to the course -- two per flatbed truck -- beginning on Saturday. About 20 buses will be used in Northern Virginia to offer additional protection to the course, according to Lt. Don Grinder of the Arlington County Police.

The county, which coordinates security during the Virginia portion of the race, has canceled leave this weekend and will use approximately three times more personnel than in past years, partly because the new course includes more heavily intersected roads such as Lee Highway and Crystal Drive and partly because of heightened security concerns, Grinder said.

"We've been doing this for 29 years, but we had to put so much more effort into [this year's race] that it felt like we were starting from square one," Grinder said.

The D.C. Metropolitan Police Department has also raised its race staffing levels from past years, but declined to provide specific personnel numbers, and the U.S. Park Police has stepped up its pre-race intelligence gathering in the past two years, acting chief Dwight Pettiford said.

A Virginia Department of Transportation employee will monitor VDOT camera feeds from several course roads on a projection wall in the department's Arlington office, said Kamal Suliman, traffic operations director for the Northern Virginia District. Views from the VDOT cameras will also be available in the marathon's on-site command center.

A Coast Guard cutter and several Coast Guard small boats will help patrol the course's waterways -- a practice that began last year -- and runners checking items at the baggage claim will need to use clear plastic bags for the third year in a row. Organizers said there were other security measures that they could not discuss for fear of compromising their effectiveness.

"We believe that what the race directors are doing is very much necessary to ensure the safety of the runners," said Pettiford of the Park Police.

Officials at last week's Army Ten-Miler similarly mounted their most robust security effort in that race's 20-year history, according to Col. Arnaldo Claudio, provost marshal of the U.S. Army Military District of Washington.

For the second consecutive year, metal detectors ringed the finish area of the race, which is located in a Pentagon parking lot. This year, the detectors were set on a higher sensitivity, Claudio said. Organizers used a mobile command center from the military's newly created Joint Force Headquarters-National Capital Region; monitors inside the command center showed near-real time video of the surrounding area taken from a camera mounted on a 40-foot mast above the truck.

Security measures also included at least three Coast Guard vessels, a sniper team from the Pentagon Force Protection Agency, triple the number of bomb-sniffing dogs on the course and plainclothes spotters in the crowd, Claudio said.

Backpacks were prohibited from the finish area. Runners approaching the starting line, which was accessible via a Pentagon parking lot, were checked with handheld wands, another policy that began last year. Many were told to check their cell phones before entering the course -- the race prohibits portable electronic devices on the course -- but some of the final runners attempting to reach the starting line were waved through because they hadn't received word of the prohibition, a spokeswoman said. The Marine Corps Marathon has no policy on cell phones.

After Metro unexpectedly closed the Pentagon station before the Ten-Miler, race officials delayed the start of the race by five minutes to allow runners to get through security lines and reach the starting area. A Metro spokeswoman said the station was mistakenly closed due to an internal miscommunication, and was reopened before the end of the race.

Several runners at last Sunday's race said the increased security was immediately noticeable.

"A lot, tons, without a doubt, more than I've ever seen," said John Beckley of Silver Spring, who ran the race for the third time and participates in about six road races year.

As the lines to get through the metal detectors grew in the hour before the race, there were isolated grumblings from the crowd about restrictions. But nearly two dozen runners interviewed before and after the race unanimously supported the race's security efforts.

"This is the most secure I've ever been," joked winner Dan Browne, who said his pre-race strides were limited by gates in front of the starting line, but said he had no complaints. "You don't see [security] like this very often, but you don't see road races by the Pentagon very often, either."

"It's a hell of a lot different here -- you ain't never gonna see [metal detectors] at a regular race," said Sgt. Maj. Victor Angry of Fort Bliss, Tex., who, after being turned away from the metal detectors because of his duffel bag, attempted to stuff both the bag and its contents into a plastic bag. "With the Pentagon right here, I can understand."

Marine Corps Marathon organizers began to increase their security efforts last spring and accelerated the effort after Homeland Security Secretary Tom Ridge's July warning that terrorists could attempt to disrupt next week's election. The race is being run in the same week as a presidential election for the first time in 16 years.

Nealis said the primary function of Sunday's race is to promote goodwill between the Marine Corps and the community, and that goal could be undermined by turning the course into "Fort Knox."

His stance was echoed by Maj. Paul Gomez, a Marines reservist who will coordinate security for the start and finish area.

"What fun is it for people to run under those conditions; they'd constantly be looking over their shoulders," Gomez said. "We just want to make sure things are as normal as we can possibly make them in the post-9/11 world."

Soldiers screened runners at the start of the Army Ten-Miler last Sunday. Marathoners for Sunday's race are being asked to arrive two hours early. The field of 13,000 runners passed through metal detectors on the way to the start of Sunday's Army Ten-Miler. From inside the mobile security command center, Lt. Col. Michael C. Kasales points out features on a computer display of the Army Ten-Miler race route.