With former president George H.W. Bush welcoming a "great generation of Americans" to the capital of the country they served and saved, a daylong series of events to dedicate the National World War II Memorial began this morning with an interfaith service at the Washington National Cathedral.

Bush, whose Navy plane was shot down in the western Pacific in 1944, praised those who served with him. "These were average men and women who lived in extraordinary times," said the last veteran of World War II to serve as president. "No matter the danger or hardship, they responded with exceptional bravery."

Bush also compared those who fought in World War II to those serving in uniform and fighting today. "Let us not be afraid to look forward with renewed faith and courage," he said.

This morning's service, which also was shown on large-screen monitors on the Mall to thousands of veterans and other guests awaiting the start of the dedication ceremony, was the ceremonial beginning of the country's largest organized gathering of World War II veterans in 60 years.

The events mark the culmination of an effort that began in 1987, when legislation was introduced to create the $175 million memorial, which is located between the Lincoln and Washington memorials. About 150,000 are expected to attend the 2 p.m. dedication. Gates for some seating areas, including those reserved for ticketed guests, opened at 8 a.m., with remaining areas opening at noon.

Following last night's rush hour, officials shut down 17th Street between Constitution and Independence avenues, closing much of the Mall to vehicular traffic for the holiday weekend. Security guards lined the fences that surrounded the ceremony's main stage near 17th Street, and helicopters ran regular routes overhead. Armed guards monitored nearby Metro stations. The U.S. Coast Guard and D.C. Harbor Patrol prepared to guard the Potomac River, and U.S. Capitol Police officers expanded their program of random vehicle checks.

With a guest list that includes President Bush, presumed Democratic presidential nominee John F. Kerry and former presidents Bill Clinton and Bush, security is at the top of the organizers' list of priorities. All attendees seated in sections nearest the stage were required to pass through screening stations and metal detectors.

And with an audience that includes many in fragile health, the logistics are more complicated than they would be for other large-scale events.

Organizers have been concerned that the risk for health problems would be increased for attendees who arrived several hours ahead of the 2 p.m. ceremony. At the dedication of the Korean War Veterans Memorial in 1995, 93-degree temperatures resulted in one cardiac arrest and 500 cases of heat exhaustion. Today is considerably milder -- with highs expected to be in the mid-70s -- but the crowd is also expected to be considerably older.

Officials encouraged ticketed attendees to take shuttle buses to get to the three seating sections for the event. The shuttles were running from the Metro Center, Smithsonian, Farragut West and L'Enfant Plaza Metro stations.

The large-screen monitors at two locations on the Mall -- between 14th and 10th streets and on the U.S. Capitol's West Lawn -- were set up for those without tickets to watch the ceremony. Non-ticketed attendees, who were not allowed on the shuttle buses, were encouraged to walk to those areas from nearby Metro stations, such as Smithsonian and Capitol South.

Free bottled water was available throughout the Mall, and nine medical tents were erected -- three between the Lincoln Memorial and the World War II Memorial; two between 17th Street and the Washington Monument grounds; two between 14th and Seventh streets; and two between Seventh and Third streets. Each tent was staffed with a doctor, two nurses, a medically trained park ranger and nine emergency medical technicians. Six of the EMTs were expected to roam the crowds near their tents. Each tent was stocked with medical supplies, defibrillators and cots and included telephone lines in case cellular telephone signals and radio signals were jammed.

Also, nine basic life-support ambulances and four advanced life-support ambulances were expected to be on hand. Medical volunteers were scheduled to be stationed at bus stops, and National Park Service and D.C. EMTs planned to circulate through the area on bicycles. A medevac helicopter also was expected to be stationed near the Mall.

Yesterday and Thursday, the first two days of a four-day World War II-themed exposition on the Mall, the extensive emergency preparations went largely untapped, according to D.C. officials. No medical emergencies were reported on Thursday, and yesterday's complications were minor.

"It's been windy, and there is some dust blowing around," said Alan Etter, a spokesman for the D.C. Fire and Emergency Medical Services Department. "We've had to irrigate a few sets of eyes, but nothing at all major."