Maryland's Renaldo Nehemiah is callled "Shark" by his coach; Frank Costello, because the young hurdler usually tracts down anyone that is ahead of him.

That is what Nehemiah did today in the UCLA Invitational at Drake Stadium, where he caught Cuba's Alejandro Casanas and went on to beat him in the world record time of 13:00 seconds.

Nehemiah's performance overshadowed the debut of Cuba's Alberto Juantorena, the 1976 Olympic 400-and 800-meter champion.

Juantorena, competing for the first time in the United States, obviously was not in top condition. He didn't have his normal withering kick in the stretch and finished third in the 400. Willie Smith, the fluid, ex-Auburn runner, was the winner in 45.55.

The meet promised to be the best ever held in this area since the days aof the Coliseum Relays and it lived up to expectations.

Nehemiah broke his own pending world record of 13.16 set April 14 at the Jenner Invitational at San Jose, Calif., in a race that brought the three fastest high hurdlers of all time together in one race.

But Casanas, whose 13.21 is the listed world mark, could not beat Nehemiah despite a rolling start UCLA's Greg Foster hit the second hurdle, staggered over the third and fell after banging into the fourth hurdle.

"If I had gotten the same start as Casanas, I would have run 12.6," Nehemiah confided to a teammate after a press conference.

As it is, the record may be submitted at 12.99 when ithe Accutrack photo of the finish is blown up and re-examined.

Nehemiah's achievement highlighted the meet during which dark clouds gave way to sunshine and clear skies.

But there were other memorable moments, such as:

Ireland's Eamonn Coghlan and Steve Scott leaning into the finish tape together in the mile. Coghlan was judged the winner by the barest of margins; both were timed in 3:57.0.

Houston McTear, once considered the logical claimant to the mythical world's fastest human title, winning the 100 in 10.17. McTear, by his own admission, had been blown out of races this season. But now he has to be reckoned with again.

Clancy Edwards, the former NCAA and AAU sprint champion from the University of Southern California, running down Cuba's Silvio Leonard in the 200. Edwards won in 20.51 after finishing a badly beaten sixth in the 100.

Lorna Griffin, representing Sports West, breaking her own American women's record in the discus with a throw of 190 feet 6 inches.

Nehemiah, nicknamed Skeets, has had only two outdoor hurdle races this year-and has set a world record each time. This follows an indoor season in which he set world records at distances from 50 to 60 yards (meters included).

Casanas came out of the blocks fast. So fast that he was recalled for a false start. In NCAA competition, the Cuban would have been disqualified. But the meet was conducted under international rules, allowimg for one false start.

"That first false start was a phych game," Nehemiah said. Once again. Casanas was out fast and had a half-meter lead over Nehemiah, who closed in at the fourth hurdle and took the Cuban by the sixth. Casanas was a meters last year and was ranked No. 1 in the world. 3.

"I think he (Casanas) jumped by two yards," Nehemiah said. "I was shocked and panicked and then I knew I had to go get him. I straightened up a bit. But his being ahead of me helped me. I was running a world-record pace for the first 60 meters."

In the 100, McTear got his usual good start but Leonard, No. 1-ranked in the 100 last year, was right with him. McTear did not fold as he sometimes does in the latter stages of a race and held off Leonard, who was timed in 10.18.

Juantorena, 6-foot-2, 185, did not lose at 400 meters last year and was trandked No. 1 in the world. He was incontention on the backstretch but could not match Smith's stetch sprint and faded to third behind Herman Frazier, who got the bronze medal in the 400 behind the Cuban at Montreal.

"May is not my month," said Juantorena, a gracious loser. "I don't run well until June or July."

He will return to the United States for the Brooks meet June 9 at Berkeley, Calif.

The mile was more of a strategic race than one in which the runners were determined to get a fast time.

Jeff Jirele of the Santa Monica Track Club was the pace setter for the first 2 1/2 laps. Then Steve Lacy went into the lead followed by Marty Liquori, Scott and Coghlan.

Scott, the former UC-Irvine runner who had timed 3:55.3 last week at Drake, jumped the pack on the last turn and had the lead at the lead of the stretch. But Coghlan, the world indoor record holder (3:52.6) and a strong kicker, closed in-andthey both lunged into the tape together. CAPTION: Picture, Renaldo Nehemiah, left, crosses final hurdle ahead of Cuba's Alejandro Casanas, right, in world-record time of 13.00. AP