The Washington Redskins already are convinced that their new conditioning and strength coach, Dan Riley, has had a dramatic impact on the team since he was hired last winter. But just to make sure, most of the veteran players went for a dip yesterday in the oversized whirlpool at Redskin Park.

"Dipping" is the players' nickname for a scientific test called hydrostatic weighing, which determines what percentage of a person's total body weight is fat.

The tests, conducted by the Fairfax-based Institute of Human Performance, will be compared with last year's results. It is a way for the Redskins to pinpoint which players have too much fat and not enough muscle and which have benefited most from Riley's high-intensity strength program.

"If people haven't been doing their offseason work, especially those not living in the area, it will show on this test," Coach Joe Gibbs said. "It's a way for us to tell where we stand and who needs to improve."

The dipping tests were just one sign of Gibbs' seriousness about his team's need to get much stronger. Another is Riley's title. He is a full-fledged assistant coach, with complete staff privileges.

"The guy is something else," said young linebacker Mel Kaufman, who has gained five solid pounds after working with Riley for three weeks. "He really relates to the players and he can motivate you. Lifting is not fun at all, but he makes it seem better than it should be. I know I need to be pushed and he can do it without acting like some kind of drill sergeant."

The players were intrigued by their whirl in the pool.

First, each was weighed individually. Then, wearing only shorts, the player entered the pool and sat on an oversized scale that hung from the ceiling. He was told to release as much air from his lungs as possible before sticking his entire body under water and expelling more air. As he hung suspended in the water, a technican weighed him.

That water weight is generated by the player's muscle, bones, organs and hair, not his fat content. After, among other factors, the amount of air still remaining in the body (residual volume) is taken into account, the player can be told his lean (nonfat) weight and how it compares to his regular weight.

"A good figure is 10 percent of the body weight being fat," said Dr. Paul Davis, the institute president. "Five percent or lower is exceptional. We've found that many running backs and wide receivers range from 1 percent to 5 percent."

Some impressive results: tackle Joe Jacoby, weighing 302 pounds, had a fat content of only 15 percent. Linebacker Monte Coleman, weighing 235 pounds, had a fat content of 5 percent.

Down the hall, meanwhile, Riley continued his workouts with Redskins as rock music blared from a radio. Riley's is different from most team weight rooms, where groups lift together. He believes in an individual, one-on-one supervised approach.

And his technique is refreshingly stimulating. To add weight to the Nautilaus machines, he'll jump on board as the player does his exercise. He is constantly talking, prodding, encouraging and consoling his subjects, pushing them, as tackle Mark May put it, "to places we wouldn't get to if we were doing this on our own."

Riley, author of four books on the subject, matter of factly says he is the best there is at his job. He does not try to make the players into weight lifters or body builders. Instead, he has molded his theories to reach one goal: "to motivate them to train and stretch to make them less vulnerable to injury."

"Anyone can make someone stronger," he said. "It's happening in Ys and health clubs everywhere. But what difference does it make how much you can bench press? Many programs fail because they want a guy for two or three hours at a time. We use a high-intensity concept that isn't so rigidly structured that it becomes boring. We want to get them as strong as possible in as little time as possible and prepare them to play football."

Gibbs is fascinated by Riley's work. He went so far as to proclaim during last month's NFL draft that rookie after rookie had a chance to make the team "as soon as he gets working with Dan and gets stronger." Riley has become, in Gibbs' eye, the Redskins' nearly secret weapon in their attempt to catch up with the league's more powerful clubs.

But that weapon was on the verge of changing professions when the Redskins came calling last January. "I was ready to leave Penn State, because the thrills and recognition were gone," said Riley.

"But I was really impressed with the commitment Joe Gibbs and Bobby Beathard were making to improving the strength program here. This really is a new position in the NFL, because many teams only have a token strength coach or a guy who also sweeps the parking lot."