Canary-yellow Rolls-Royces and Newport mansions once were the primary playthings of the rich, ways to celebrate the beneficence of the free market and the spoils of power. Nowadays, sports franchises are the flashiest ornament of all.

The new U.S. Football League, which begins its first season today, has provided another dozen jewels for the flaunting, and their owners are gambling that the value of those baubles will burgeon with time.

So far, the owners have good reason to think they have invested wisely.

The USFL is enjoying all the good fortune that the World Football League did not. Within two weeks of its official founding last May, the USFL secured a $20 million television contract with ABC. A deal with ESPN soon followed. Top collegians, like running backs Craig James (Washington) and Tim Spencer (Chicago) and wide receivers Anthony Carter (Michigan) and Trumaine Johnson (Chicago) signed lucrative contracts. Others, like running back Eric Dickerson, are still considering huge offers.

The signing of Heisman Trophy winner Herschel Walker was, of course, the latest and most publicized stroke of fortune. It took the American Football League five years to sign a player of Joe Namath's caliber, but the USFL suspended its own rules and risked the ire of the NFL, the college coaches and the fans to get Walker at once.

Even as he answered harsh questions about Walker, USFL Commissioner Chet Simmons knew that the controversy would fade and Walker would remain, at least for three years, a USFL asset. By choosing to pursue Walker, who was still an undergraduate, Simmons reasoned that he would rather be a controversial success than a canonized flop.

But the battle for success and solvency has not yet been won. There are dangers the league must avoid and goals it must attain.

"We've got to get the fans in the stadiums and we've got to get them to come back," said Simmons. "To do that we have to have a major habit change, from watching in the fall to watching in the spring and summer. That's the essence of it."

Simmons said that if the teams succeed in drawing 30,000 fans for every game, they should come close to breaking even. In addition, each club can expect approximately $1.5 million in television and radio revenue in the first two years.

Berl Bernhard, one of the Federals owners, said, "From our standpoint, we had targeted an average of 26,000 as livable. We knew we would take a loss, but we thought it was a livable one. I think it's possible that we may even average 30,000."

While the Denver Gold has already sold more than 30,000 season tickets, the Boston Breakers have managed to sell only 3,600. Simmons presides over a $16 million fund established by the league owners to bolster the weaker franchises if the need arises. So far, no one, not even the Boston owners, has required such subsidies, and the league plans to expand from 12 to 16 franchises next year.

The ABC contract is for two years, but Bernhard says that his colleagues are thinking beyond 1984.

"The early concept was to see how we did after two years," said Bernhard. "But no one is looking at it that way anymore. Everyone is assuming we'll go way beyond two years."

The league obviously will fail if it does not attract fans, both at the stadiums and in front of television sets. Much of Simmons' confidence about the future of the USFL is based on a marketing analysis commissioned by the league to see if fans would be interested in spring football. The analysis indicated that 53 percent of the public would prefer a weekend football game to a baseball game in the March-July period.

Some people may turn out to the stadiums or turn on the set just to see what the USFL is all about in its first weeks, but to retain a level of interest that promises future profit, the league must be good enough to compete with baseball on NBC and pro basketball on CBS.

Jim Spence, senior vice president of ABC Sports, said he expects the USFL to win a 5 or 5.5 rating (as compared to a 6.3 for baseball in the past two years).

"We're committed to carrying the league for two years," said Spence. "Whether we continue or not will be based on whether we think it has the potential to compete and get better. It all comes down to what's on the field. If the USFL is competitive and puts on exciting games, it should succeed."

ABC will be trying to bring more "intimacy" to the game by putting microphones on coaches and using live interviews from the locker rooms during halftime and along the sidelines during the game.

The network will chase the highest ratings by choosing the most attractive game of the week. As a result, Herschel Walker stands to make money not only for the New Jersey Generals' J. Walter Duncan and the opposing owners--visiting teams reap 40 percent of the gate--but for ABC as well. ABC may see fit to have him appear on Sundays as often as the Rev. Jerry Falwell.

Mike Faulkiner, the Federals' former director of player personnel and now an assistant coach with the New York Jets, said the league must build cautiously to maintain a competitive balance.

"The teams in the WFL went out and got too greedy," said Faulkiner. "They signed players they couldn't really afford. And what that did to the competition was a disaster. The whole thing went out of balance."

Sources who did not wish to be quoted by name have accused Chicago Blitz Coach George Allen and Generals Coach Chuck Fairbanks of trying to do too much, too soon, with too much money. Before the draft, the teams made a gentlemen's agreement to limit their salary budgets, but some teams appear to have been more gentlemanly than others.

One outsider who is experienced in "start-up operations" is Earl Foreman, the commissioner of the Major Indoor Soccer League. He said the USFL's signings of major college athletes was "an essential ingredient for success."

As to whether the USFL will survive in the long run, he said, "It's like looking at election results at 6 o'clock. You won't have any answers for a year or so. It's a long pull."