By 3:30 yesterday afternoon, most of the seats in the cavernous Washington Convention Center were filled, while outside fleets of buses continued disgorging throngs that gathered for the first Billy Graham Crusade here in 25 years.

When the service began 30 minutes later, 21,000 people had crowded into the center, some sitting on the bare concrete floor, others standing to get a better view. Late-comers seated in the back of the hall watched the events on the platform, more than a block away, on 10 giant screens.

The volunteer choir of more than 3,000 opened with "Bless His Holy Name," and the crowd rose and applauded as Graham and his entourage, which included Vice President Bush and the past and present mayors of Washington, made their way to the simple platform draped in blue and gold.

"The purpose of this meeting is to present the Gospel of Jesus Christ," said Graham, "how you receive Christ and how you apply that Gospel to your own community."

That was clearly what they had come to hear. As Graham preached an hour-long sermon on the emptiness of a lack of commitment and on Christ as the centerpiece of a happy, fruitful life, heads nodded in agreement. Hushed "amens" and loud, spontaneous outbursts of applause interrupted the sermon. Many in the crowd carried well-thumbed Bibles.

Graham, in a dark blue suit, was folksy, affable, comfortable, at home. "I feel like the man who entered his mule in the Kentucky Derby," Graham joked with the crowd. "Someone said, 'You don't expect him to win, do you?' 'No,' he said, 'But look at the company he'll be in.' "

He spoke to a largely white audience with a sprinkling of blacks and Asian Americans. The middle-aged and elderly greatly outnumbered the young, many of whom carried babies or pushed children in strollers. Most had come dressed in their best Sunday clothes.

Volunteer usher Alice Walker, an elderly member of Hemingway Temple AME Church in Northwest Washington, held a stack of programs in her white-gloved hands and wore a smile on her face. "I went to the Graham crusade in New York in the 1940s," she recalled. "He was wonderful. It's very exciting to be here. I'm interested in ushering because you meet lots of people, and I'm interested in this crusade because I'm a Christian."

Graham told the crowd, "Christ died for you, he wants to help you . . . . But you must do something. You must repent of your sins."

Repentance "means a changed life," he said, adding that Christ should be accepted as a matter of faith.

Then he began the call for a commitment to Christ. "I'm going to ask you to do it today," he said. "I'm going to ask you to get up out of your seat and come down and stand in front of the platform.

"If you're with friends and relatives, they'll wait," he continued in persuasive tones. "If you came with a group, they'll wait . . . . But you get up and come, hundreds of you, black or white, Jew or Gentile . . . you come."

And 1,309 came, streaming out of every corner of the auditorium: couples holding hands, some leaning on a partner, two young Vietnamese women in the silk dress of their homeland. For five minutes they streamed to the front, as the choir and most of the congregation softly sang "Just As I Am." Some had tears in their eyes; some smiled.

Hundreds of counselors, trained volunteers from area churches, stood ready to guide them to special counseling rooms. Each person who came forward was asked to fill out a card, indicating their church preference. Other volunteers will sort the cards overnight and compile lists, which then will be forwarded to the church nearest the person's home for follow-up.

In the very last row in the massive auditorium, at the top of the bleachers, Wilette Ivey, a 16-year-old member of Rhema Faith Center in Tysons Corner, stared at the service on a nearby screen.

"I came with my mom, and there are a lot of our church members here in the choir and ushering and doing lots of other things," said Ivey. "I came because we talked about it in my church and the minister asked people to participate."

Bob Sheldon, 33, of Harvester Presbyterian Church in Springfield, stood in an aisle to get a better view of the program and to await the moment when he would be called to the front to fulfill his role as a counselor.

"I attended a series of classes, one each week for a month, to train for this," Sheldon said. "I came because I am a Christian and I wanted to do my part."

Those in the audience who did not speak English could, for $8, rent a receiver for simultaneous translation of the sermon into Spanish, Korean, Vietnamese, Ethiopian, Cantonese or Mandarin.

The service itself was free and open to all, but an offering was collected just before the sermon. The local sponsoring committee of religious leaders that invited Graham also raised $1.5 million to pay for the crusade. Graham's organizations always publishes a detailed financial statement at the close of a crusade.

Security at yesterday's service was unobtrusive. Tex Reardon, the crusade's chief security officer, said that while "we are much more aware [of security problems] than we would have been a year ago," no problems are anticipated. About 12 off-duty D.C. police officers were employed by the crusade to provide security, he said.

A contingent of Secret Service agents, accompanying the vice president, flanked the platform.

In remarks before Graham's sermon, Bush linked religion and patriotism. "The strength of our nation is in our faith. Our nation will be strong as long as faith is strong," he said.

"We do believe when all is said and done that we are indeed a nation under God," he said. And he welcomed Graham to Washington, "the capital of this nation . . . the last best hope of man on earth."

Graham's Minneapolis-based group has organized thousands of crusades over the years with set techniques so thoroughly mapped out that they are almost like spiritual Tupperware parties.

The key is the selection and training of volunteers, thousands of whom have been recruited for this week's events with the help of Washington area ministers and churches.

Preparations for the crusade began more than a year ago, and they paid off yesterday. More than a 1,000 volunteer ushers, some dressed in starched white uniforms, handed out programs and helped with seating. An estimated 3,200 counselors and supervisors were trained in addition to the 3,500-member choir.

In addition to being promoted in the 630 cooperating churches, the crusade has been widely advertised on television and radio.

"Now we're going to be here every night," Graham said referring to the eight-day visit. Noting that the Convention Center cafeteria will be in service throughout the week, he said, "You can come right from work and get a bite to eat here."

Graham said he has prepared a special message for the young at tonight's session, which begins at 7:30. The crusade will close next Sunday with a service at RFK Stadium.