HOW TO MAKE THE CUT : Don’t drop the ball with coaches around (see above) : Explode at the ballcarrier, or at least hit really hard : Show speed, strength --’something, anything’

A football shoots out of the Jugs machine and flies about 70 yards downfield where the rookie stands waiting. He wants to grab it at just the right moment, but in his anxiousness he reaches too soon, and it bounces off his chest like a quarter off the floor.

“You can’t run before you catch the ball,” the coach yells. The rookie claps his hands in disgust and trots back to the end of the line to wait his next turn.

A simple mistake, perhaps. But for the 58 rookies and 16 free agents who arrived at the Dallas Cowboys’ training camp at Cal Lutheran on July 6, no mistakes are simple. Second chances at this point are scarce.

All but about 10 newcomers will be home, not in Dallas, when the season begins Sept. 8.

“There are so many guys competing for just a few spots,” said guard John Ionata, the Cowboys’ 10th pick out of Florida State. “And everybody out here is doing whatever they can to win one of those spots.”

The trick is to find a way to catch the coaches’ attention.

“They have to show something that indicates they can develop into a solid player,” Coach Tom Landry said. “We look for speed, strength, quickness, competitiveness--something, anything--that makes them stand out.”

Said Al Lavan, who coaches the running backs: “A player will catch your eye. Usually it’s not one thing that determines it. Over a period of time you watch them improve, and you come to a point where you have an opinion of their abilities.”

Lavan, who is working with 10 newcomers, knows that there are only one or two open roster spots for running backs. And the players know that Darryl Clack, the No. 2 pick out of Arizona State, who has been projected as a backup to Tony Dorsett, may sign at any time.

Linebacker coach Jerry Tubbs is looking for players who can “get rid of the block real quickly,” who can “explode into the ballcarrier,” but most of all, “we want somebody who really hits hard,” he said. There is only room on the roster for one or two of the 12 men he’s working with.

That leaves free agent Henry Walls’ chances pretty slim.

“Yeah, I’m a long shot,” said Walls, a 6-2, 222-pound graduate of Clemson.

But he was no more of a long shot than a free agent named Drew Pearson, who showed up at camp 13 years ago. He retired in 1984 as Dallas’ all-time leading receiver.

Or consider Everson Walls, a sixth-year cornerback on the Cowboys, who signed as a free agent out of Grambling in 1981. He not only broke into the lineup but was a Pro Bowl selection from 1981 to ’83.

“These kids have a chance, but it’s too early to tell,” Landry said. “Many great players have come in the late rounds or as free agents.”

Added Ernie Stautner, the defensive line coach: “Even for the veterans, there are no guarantees. There’s always someone competing for your job. And if I find someone who’s doing well enough, I might keep him.”

But the odds against are sobering, especially for those such as kicker Kelly Potter, a 1985 graduate of Middle Tennessee State who was cut from the Buffalo Bills in the preseason last year. His prospects don’t look much brighter this time around.

Veteran Rafael Septien, although bothered by back problems, is still Landry’s No. 1 placekicker. And because the Cowboys probably will keep only one other kicker, Potter will have to beat out three other prospects, including No. 4 pick Max Zendejas, who signed Friday.

So Potter, a native of Nashville, is prepared to fall back on his experience in rodeo, sales or construction. A similar question faces most rookies and free agents: What do I do if I can’t play in the NFL?

Several will try out for United States Football League teams, and some will keep returning for NFL tryouts, but eventually they will have to “look for a regular job like anyone else,” said Stan Gelbaugh, a 6-3 quarterback and the Cowboys’ sixth pick.

Gelbaugh graduated in May from Maryland, where he led the Atlantic Coast Conference in total offense with 2,475 yards, breaking Boomer Esiason’s single-season school record. Gelbaugh comes from a tradition of success. Esiason, a 1984 Maryland graduate, is the Cincinnati Bengals’ starting quarterback, and Frank Reich, an ’85 graduate, is a quarterback with the Buffalo Bills. Gelbaugh is looking for a spot behind veterans Danny White and Steve Pelluer.

Other possible alternate occupations: Ionata, a finance major, might work in a bank; guard Lloyd Yancey, the seventh pick out of Temple, might try to become a businessman; defensive back Darryl Austin, a free agent from Texas A & M, has thoughts of becoming a probation officer, and running back Topper Clemons, the ninth pick out of Wake Forest, may teach social studies back home in Camden, N.J.

They are a far cry from performing in front of tens of thousands of screaming Cowboys fans in Irving, Tex., but the rookies will take their chances.

“Any time you have an opportunity to get into professional sports, it’s a dream,” Ionata said. “I’ve watched the Cowboys all my life and now I get my shot.”

Cowboy Notes

The Cowboys still haven’t signed No. 1 pick Mike Sherrard, a wide receiver out of UCLA. Sherrard was expected to be drafted by the New York Giants, but the Cowboys moved into position to draft Sherrard in a last-minute trade with San Francisco. Coach Tom Landry compared the situation to last year, when the Cowboys wanted Eddie Brown, a receiver from Miami, but lost him when Cincinnati earned the pick through a trade. Brown went on to average 17.8 yards per reception and score eight touchdowns. “This year we said, ‘We want him,’ ” Landry said. “We finally got a chance to trade for him and we took it.” . . . No. 2 pick Darryl Clack, a running back from Arizona State, and No. 3 Mark Walen, a defensive tackle from UCLA, are the only other rookies besides Sherrard who remain unsigned. The Cowboys aren’t alone. As of Tuesday, only three of the top 55 selections in the draft were signed to contracts. Without a signed contract, a rookie cannot report to an NFL training camp. . . . The veterans reported to training camp Sunday, but mysteriously missing is strong safety Dextor Clinkscale, whose whereabouts are unknown. The Cowboys have issued no comment on his absence from camp. . . . A pay television cable company in Texas began broadcasts of Cowboy practices every day from 3:30 p.m. to 5:30 p.m. The programs, which include on-the-field activity as well as pre-taped interviews, can also be seen on Storer Cable in Thousand Oaks. . . . The Cowboys’ annual intra-squad scrimmage is set for July 26 at Cal Lutheran. The team then goes to London, where it will play the Chicago Bears in the special preseason American Bowl at Wembley Stadium on Aug. 3. The following Saturday, the Cowboys travel to San Diego for a game against the Chargers and then face the Raiders at the Coliseum on Aug. 16. The Cowboys return to Dallas Aug. 21 and play their final preseason games against the Pittsburgh Steelers (Aug. 22) and the Houston Oilers (Aug. 30).