The mix of talent, to be sure, is strange and just a bit stale: there is heavy Queen and a dreamy James Taylor, raspy Rod Stewart, jazzy George Benson and the punky B-52's.

The unappreciative are also muttering that this week's rock festival in Rio, sponsored by McDonald's and Pepsi, bears more of the soul of the free-enterprise Olympics and the second Reagan inaugural than the promoters' official model, Woodstock.

But on at least one point, there can be no argument: "Rock in Rio," which opened Friday night, boasting 10 days, 29 acts, and a hoped-for 1.5 million fans in a specially built, $6 million "Rockodrome," is the largest, most extravagant, most commercialized and most mega-hyped event in pop music since . . . well, maybe since the Jacksons' Victory Tour.

That seems to be the point -- and it's a matter of national pride. "Until now, the largest music festival in the world has been the American San Bernardino festival," explained Roberto Medina, Rio's flamboyant promoter, to the Brazilian press. "But compared to Rock in Rio, it's a joke."

The local media, frenetically boostering, cannot get enough of the statistics. It seems Medina and his Artplan Promotions have spent a total of $11 million to attract 14 international and 15 Brazilian acts, and built a stadium with a 70,000-watt sound system that will hold up to 400,000 people. Fifteen hundred buses are available each day to transport fans the 18 miles from downtown Rio to the concerts, and 15,000 camping spaces have been set up nearby.

The official themes of the festival, spelled out on thousands of T-shirts and an official theme song, are the "music and peace" of Woodstock. But the drone of the statistics goes on: McDonald's, which claims to have constructed its largest store in the world on-site, hopes to sell 500,000 hamburgers; the Brazilian company Brahma expects to peddle 1.6 million liters of beer; Bob's is shooting for 1 million sandwiches; and the promoters say they will settle for a profit of $500,000.

Medina actually claims convincingly that money is not his object. The 37-year-old promoter, who is best known here for having lost money on a Frank Sinatra tour several years ago, seems more intent on "the personal and business prestige" he believes will come from proving that Rio can make the big leagues in international rock.

The sense of having to match the Yankees is strong; there is a thinly disguised fear that Rock in Rio, even with an English-language title, will be labeled Third World. "The plan is great. But will this work in Brazil?" asks one Artplan pamphlet. "In the end," it answers, "one of the objects of this project is to show here, and more importantly, out there abroad, that this country works."

Medina did seem to have had some trouble recruiting foreign talent; though the festival was meant to feature heavy rock, the final assemblage of acts appears like a kind of grab bag of whoever could come.

AC/DC, Iron Maiden, White Snake, Ozzy Osbourne, and Nina Hagen are here, but so are Taylor, Benson, Yes and jazz singer Al Jarreau, who seemed to have particular trouble defining his role. "The fact that I'm here proves that music is music," he told a press conference.

Still, Rock in Rio is a wonder of big thinking. Every imaginable crowd accoutrement has been installed in the Rockodrome. There are huge bathrooms with hundreds of permanent toilets, a small, well-equipped hospital, a heliport, public telephones and even two fountains for fans to cool off in.

In addition to the sponsors, Artplan sold exclusive television rights for Latin America to Brazil's Globo Television, transportation rights to Varig Airlines, merchandising rights to makers of shirts, sandals, hats and records, and even cigarette rights -- only the Brazilian brand Hollywood is sold on the grounds.

The on-site fast-food outlets are accompanied by two circular shopping centers, four bars, and two "video centers" where canned clips of performers are shown throughout the day, evidently in deference to those who feel more comfortable with television than live action.

On sale are not only the usual items like T-shirts and pillows, but also stereos, video games, computers, hair treatments featuring "glitter gel," and a virtually complete selection of records and tapes by the featured performers. Rock in Rio albums are available, complete with the festival's emblem and a printed boast: "I went."

Despite all the imported style, some of the Brazilian musicians managed to preserve their identity. Asked why he had chosen to wear shorts on the stage rather than get up in an elaborate costume, singer Lulu Santos replied that "the Brazilian sets are a little more modest, perhaps because otherwise people wouldn't have the courage to go out on the street afterward and buy bread. The country is poor."

Behind it all, though, is the upstart's mania with Doing It Right. With a self-congratulatory flourish, Artplan opened the gates of the Rockodrome Friday exactly at noon, then after repeated admonitions to the casual Latin crowd, the festival began precisely on time at 6.

"We are beginning one of the great moments of our lives," boomed an announcer in Portuguese over the computer-tuned sound system.

"Heavy metal, heavy metal," chanted the front ranks of the crowd, in English.

"Because we are here, Brazil is going to live a new dawn. The dream is not over," said the announcer.

"Heavy metal!" screamed the crowd.

In the end, a few things didn't quite come off. A zeppelin that was supposed to shower the crowd with rose petals never appeared, and the promised 500 doves turned out to be a straggling handful. Despite the hype and incessant coaching on the spirit of Woodstock, much of the crowd for the first night's heavy-rock-dominated show was rough and aggressive. Rocks and bottles were tossed around the first rows and a Brazilian singer who tried to get away with a soft local ballad was loudly booed.

A lot of the gimmickry, however, seemed to take hold. Organizers managed to distribute tens of thousands of single, Day-Glo green gloves before the concert began, and on cue, thousands of fans raised glowing fists for the Rock in Rio anthem as the television cameras rolled for history, the folks back home, and perhaps principally, those "out there abroad."

"If it's not any good," Medina told a Brazilian reporter, "it's not my fault." Don't blame it on Rio.