Whenever there has been an opportunity to make money, enhance a reputation or try an innovation, the National Football League has been on top of it.

But now the league of Monday night football, instant replay and huge television contracts has outdone itself. It has taken the biggest financial leap of all professional sports leagues into the most fertile sporting ground of all, the '90s.

The landscape of the NFL, once a sprawling, mundane plateau, has become a startling series of hills and valleys. Commissioner Paul Tagliabue, who hasn't been in office even a year, has affected more changes than Pete Rozelle did in perhaps his last five years on the job.

There is the largest television contract in the history of sports -- $3.66 billion from three networks and two cable networks over four years, a 93 percent increase over the previous contract. There is an unprecedented international foray -- the World League of American Football -- that will give the NFL a presence no other U.S. sport has ever had abroad. There are bigger-than-ever contracts for players -- an average of about $300,000 last season -- and more movement than ever with Plan B free agency.

There are lawsuits and countersuits, but in the midst of labor unrest, there is the belief from both sides that it is finally time to solve a three-year squabble between players and management that has festered since the 1987 strike. There is stiffer drug testing and, for the first time, random, year-round steroid testing. There is a longer season, more playoff teams and an off week for every team.

And, yes, there still is instant replay, with a two-minute time limit on discussion.

"If you coast, you can only go downhill," said Los Angeles Raiders executive Al LoCasale. "The changes are good. . . . They add a little life."

Everything begins and ends with the phenomenal amount of money the NFL received in its TV deals late last winter. The four-year package nearly doubles each of the 28 clubs' annual take from $17 million to an average of $32 million per year over the four years.

Where does this money go? Most of it goes to pay the biggest bill there is -- player salaries. According to the NFL Management Council, 96 percent of television revenue in recent years has been spent on player salaries. Of course, there are other sources of income, including ticket revenues, sky box sales, concessions and licensing. Now, with the tremendous increase in TV money, there would be the expectation that salaries would escalate just as fast. That's what players and agents want, of course, but that's not what owners want.

In fact, Cleveland Browns owner Art Modell said that, without citing specific clubs, 16 of the 28 teams lost money last year. The average cost of running a team a year is $35 million "or higher," he said.

"You don't cover all costs by TV money."

But this TV money changes things. Player payrolls "definitely" will rise, said John Jones, spokesman for the Management Council, but some of the TV money also will be used to "make up for the red ink of the last season or two," he added. The NFL Players Association, which says it has decertified as a union but still works on behalf of the players, expects the average salary to rise as high as $360,000 this year.

Already, agents have tried to take advantage of the big money flowing from the TV deals. Representatives of many of the players holding out from training camps this summer have said they know owners have more money, and they want some of it for their players. There is no clear evidence that this is happening, at least not yet; the NFLPA, although it expects an increase, is taking a wait-and-see attitude and believes the money might not truly manifest itself in player paychecks until 1992 or 1993.

The labor situation is anything but clear. There are three lawsuits pending based on the general issue of player movement, while Plan B free agency continues to confound. Because those players not protected by NFL teams are available to any other team, there is competitive bidding for their services. In many cases, Plan B free agents end up making more money than some starting veterans on the teams they join. What this does for team morale is anyone's guess.

"The whole system is out of whack," said M.J. Duberstein of the NFLPA. "The market is still built on the premise that the only players negotiated for are the ones deemed to be at the low end of the roster. That's bizarre."

Meanwhile, there is the hope that the TV money will get both sides in the contentious labor struggle to sit down and agree on a contract, which players have been without since September 1987.

"We assumed there would be a TV hit," said Jack Donlan, executive director of the Management Council, after the TV package was announced. "We didn't assume it would be this great. We would think that the union would like to devise a system to get {the money} to the players."

Five months later, that still has not been done.

TV money also was instrumental in changing the league's schedule and playoff structure. To increase exposure, add commercials and, of course, make more money, the league inserted an extra week into its schedule for this season and next and two extra weeks into the schedule for 1992 and 1993. Teams still will play 16 games, so everyone gets one week off the next two years and two weeks off after that.

The season begins Sept. 9. Off weeks are grouped by division so rivals can't complain a team received an advantage with the timing of its week off. The Washington Redskins, Philadelphia Eagles, New York Giants and Phoenix Cardinals all will have the same Sunday off -- Oct. 7 -- while the Dallas Cowboys will have the same Sunday off -- Dec. 9 -- as the other three teams that finished last in the five-team divisions.

This creates an interesting situation for the NFL and the networks. During the weekend that the NFC East is off, the major markets of New York, Philadelphia and Washington will not have their local teams on TV.

The league considered this but decided there still was more money to be made by adding the extra week, even if ratings drop in the East because the local teams aren't playing. The NFL believes Redskins fans still will tune in for, say, the Chicago-Green Bay game that weekend.

"We gave the greater priority to making more games available from around the country," said Dick Maxwell, the NFL's director of broadcasting services. "We want to spotlight the national nature of our game of pro football. We're very fortunate that our sport is very national in its attraction."

Along with the off weeks came the addition of two more wild-card teams, one from each conference. (The NFL, with 12 teams in postseason play now, still will have fewer teams playing after the regular season than any big-time professional league but Major League Baseball.) It all ends with the 25th anniversary of the Super Bowl, Jan. 27 in Tampa.

These changes threaten to create havoc with viewing habits and practice schedules, but it's just a sign of the times for the league.

Said New York Giants General Manager George Young: "This is progress, and part of it is selling the product. You know, the owners do have a right to make a profit. Why do they have to apologize about that?"