Gradually, the trickle has become a flood. Numerous stars have left the U.S. Football League and followed the current into the National Football League, thankful for a league that is stable and hoping their bodies won't break from back-to-back seasons.

How vast has the drain of stars been on the USFL? Big enough to provide a boon to the NFL. Consider the USFL's most significant losses:

*Kicker Tony Zendejas (Express to Redskins) was the USFL's field goal leader in 1985.

*Wide receiver Trumaine Johnson (Outlaws to Chargers) caught 90 passes in 1984 before a season-long contract holdout in '85. He reportedly paid $500,000 to buy out his Outlaws contract.

*Running back Mike Rozier (Bulls to Oilers), the former Heisman Trophy winner, gained nearly 1,400 yards in 1985, second most in the USFL.

*Running back Maurice Carthon (Generals to Giants) totaled nearly 1,800 yards the past two seasons, proving that more than one running back can thrive in Herschel Walker's Jersey.

This list does not include Birmingham running back Joe Cribbs, who led the USFL in rushing in 1984, then ran for more than 1,000 yards in 1985. According to his agent, Cribbs recently paid $750,000 to buy out the rest of his USFL contract so he might return to the NFL (the Bills own his NFL rights).

Nor does this list include quarterback Bobby Hebert, the USFL's career passing leader, whose USFL contract expired with the Oakland Invaders and who is trying to arrange a deal with one of several interested NFL teams.

And, perhaps most damaging of all for the USFL, the agents for two of the league's most coveted players -- quarterbacks Jim Kelly and Steve Young -- are talking about breach of contract and say they are considering taking their clients to the NFL, too.

The fact that Anthony Carter, the electric wide receiver for the Invaders, talks of escaping from the option year of his USFL contract in 1986 to play for the NFL team that owns his rights -- Miami -- adds to an already crystal-clear picture.

"The Invaders have until Aug. 1 to decide whether to pick up the option. If they do, Anthony will play for them next year," says Bob Woolf, Carter's Boston-based agent. "If he had his preference, though, Anthony has always wanted to play for Miami."

Two weeks ago, USFL Commissioner Harry Usher said of the exodus of USFL stars, "It's not such a critical thing to the league. New stars will develop in our league." Usher also said recently that the NFL's interest in these players was a "compliment" to the USFL.

Divergent views have emerged about the exodus of drawing-card players from the USFL. One view relates to the USFL's $1.32 billion antitrust suit against the NFL, enjoining the NFL from appearing on all three television networks. The trial date tenatively is scheduled for February 1986.

"That lawsuit is the biggest obstacle of all in moving from the USFL to the NFL," says Greg Lustig, the Ohio-based agent for Kelly. "The NFL is being extremely cautious (in pursuing USFL players), except in those situations like Los Angeles (Express), where the team is anxious to get rid of anybody."

"I don't think the NFL is being cautious at all," says Art Wilkinson, the Philadelphia-based agent for Rozier. "The NFL is the master of the smokescreen. I think the NFL is doing exactly what it always does: say one thing and do another. The NFL is not being cautious at all, but just legally expedient or even rising to the level of being politically expedient."

Don Weiss, executive director of the NFL, says, "It would not be appropriate for us to make a comment other than to say that we are not going to engage in any conversations with players unless we are certain that those players are contractually free."

Responding to Wilkinson's charge that such a posture is merely a "smokescreen," Weiss added, "That's one opinion, and an erroneous one."

Meanwhile, the USFL continues to make cutbacks. San Antonio released all 46 of its players earlier this week. The league office and numerous teams have made cutbacks in top personnel. At present, only five of the 14 teams have public relations directors.

"Usher has told us there are three players the league can't do without: Herschel Walker, Jim Kelly and Doug Flutie," Lustig said. "But if Birmingham lets Joe Cribbs go, and if (quarterback) Vince Evans becomes available, and if Arizona tries to unload (quarterback) Doug Williams, that tells you the owners are trying to go back to basics."

Usher recently gave Leigh Steinberg, agent for Young, clearance to negotiate with the Tampa Bay Buccaneers, who possess Young's NFL rights. Steinberg says Usher did not, however, give him the right to sign Young with Tampa Bay. Young had signed a contract with the Express worth a reported $40 million.

"The point I'm making is that we're not talking about a technical breach in Steve's contract," Steinberg says. "There were clauses in his contract designed specifically to avoid the kind of situation that occurred this season.

"The conditions Steve bargained had to do with the quality of coaching he would receive, with quality management and with an owner who owns businesses off the field that Steve would be involved in. It did not have to do with playing in the Coliseum with 3,000 fans, with few or no reserves on the team, with no TV or radio contract to speak of and with creditors lined up around the block . . . I conclude that his contract has been breached and that (the USFL) has no right to tell him that he can't sign (with the NFL)."

Kelly's contract with the financially troubled Houston Gamblers was breached, says Lustig, his agent, "because he wasn't paid the last two weeks of the season and the playoffs." Lustig says the league has said it will assume responsibility for Kelly's contract if the Gamblers are unable to make payments. Lustig said he is waiting to find out if the Gamblers will be sold and moved to New York, which he claims would be a bonanza market for a player such as Kelly, who has two years on his contract.

"If the Gamblers aren't sold and moved, I would try to solve Jim's contract with the USFL. If I can't work it out, I would take the USFL to court. But if the team goes under and the league goes under, all you end up with is a lawsuit against a bankrupt league. It's sort of a Catch-22," Lustig said.

Although professional football players generally are paid only during the season, USFL owners are planning to begin paying their players 30 percent of their salaries for next season between March and the beginning of training camp. This will be done so players won't have to go 14 months without receiving a check.

"I don't think it's reasonable to wait 14 months to see if there's going to be a league. We can't make up for 14 months of lost income, lost opportunity and lost playing time," Lustig said. "Unless we can get all of these answers, we have to look at other options. We don't believe (30 percent) provides us with enough incentive to stay with the league, not on a superstar's behalf."

Wilkinson, Rozier's agent, said, "I think Jim Kelly and Steve Young are being injured, but not from the pocketbook standpoint, because their contracts are guaranteed, or from the standpoint of a 14-month layoff. It's because of their being associated with being circus performers and not football players. In the USFL, they will be seen as part of a sideshow, not the main show."