Ronald Reagan rode into his coronation decked out in summer white today, and, while the cheers poured over him, he held aloft his 2-year-old grandson, grinned and said to him, "Cameron, I'm here."

The former California governor and Hollywood movie star, as demure as the homecoming heroes in one of his campus films, told a few jokes and kept the weighty speechifying to a minimum during his welcome in a hotel lobby.

In a bantering echo of a Martin Luther King Jr. trademark, he delivered his "I Had a Dream" speech.

"I had a dream the other night. I dreamed that Jimmy Carter came to me and asked why I wanted his job. I told him I didn't want his job. I want to be president."

Reagan seemed momentarily disoriented and overwhelmed by the welcoming spectacle at the city's Renaissance Center, where the crowds were fragmented on many levels in the soaring inner lobby of the Plaza Hotel. The modern complex is a symbol of the troubled city's struggle to revive itself.

"I don't know exactly which way to face." Reagan said as he turned, craning his neck to look around at the beads of people receding into the distance, on circular balconies, up curved staircases, slowly rising or descending on escalators, broken by sculptures and the shapes of TV equipment, and up five stories to a glass skylight.

But the GOP throngs weren't a bit confused. They had the Straw Hat Band playing 'Grand Old Flag," Yankee Doodle Dandy," and "California, Here I Come." Reagan's daughter Maureen led vigorous, accelerating cheers, and posters of Reagan's lopsided cowboy smile formed visual echoes throughout the architectural confusion of the showcase lobby.

Reagan, accompanied by his wife, Nancy, had endorsed the GOP platform promptly upon his arrival at the airport, "especially its economic plank."

Noting that nearly 300,000 men and women of the auto industry are out of work, he called his party "a growth-oriented, productivity-oriented alternative to the high unemployment, high inflation and high taxes of the Carter administration. We need to put America back to work again . . ."

In his brief speech at the hotel, Reagan called for "a crusade in this country." He expressed the hope that "when we leave this city, the people of Michigan and of Detroit [traditionally Democratic territory] will know we are determined in our hearts to change [their plight] and make America great again."

Euphoric Reagan supporters waved cowboy hats and wore buttons (Reagan Will Crunch Carter's Peanuts) and hand-lettered posters (For a Better Today, and a Better Future, Vote for Reagan).

"This just might save our country," whooped Vera Manning, a gray-haired California delegate wearing a cowboy hat and a "Ronnie's Angels" button.

"We're too united to blow this one," said Kyle Lee, 18, a Youth for Reagan from Amarillo, Tex.

There was a smattering of pro-and anti-ERA demonstrators at the reception.

California Lt. Gov. Mike Curb kept the crowd entertained before Reagan's triumphal arrival. At one point, he said: "I just got word that his car has arrived. . . ." When the crowd interrupted him with cheers, he tried to calm them, saying, "It'll take him a couple of minutes to get out of the car."

Some in the crowd, taking that as an allusion to the ever-sensitive subject of Reagan's age -- 69 -- tittered. Curb hastily added, "He moves as fast as anyone here!"

Reagan changed into a dark suit for an address to the delegates later in the day. In the city's civic center, Cobo Hall, Reagan stood on a stage in a ballroom, totally obscured from most of the audience by a crescent of TV cameramen and reporters.

He added a few new quips to his earlier statements. Discussing the country's economic woes, he said, "Jimmy Carter is doing his best. That's the problem." And later Reagan said, "Carter is going to stand on his record. That's to keep us from seeing it."

Continuing his pitch to the Democratic constituency of blue-collar workers, he charged that Carter's administration has "betrayed" the nation's working people.

Reagan's schedule today also included a social visit with former president Gerald Ford, a one-time political rival, who was celebrating his 67th birthday.