On July 11, three days after this year's Wimbledon championships end, Guillermo Vilas will play Dean Martin Jr. on the Centre Court of the All England Lawn Tennis and Croquet Club. With cameras rolling and the area packed with "extras," they will simulate the final of the world's premier tennis tournament for an upcoming Paramount movie, "Players."

That, alas, will be Vilas' next appearance on Centre Court. Yesterday, for the second year in a row, the Argentinian left-hander was beaten in straight sets in the third round of the real Wimbledon.

Last year, the culprit was Billy Martin. This year it was Tom Okker, the erstwhile "Flying Dutchman," who played with all his old swiftness and fidgety efficiency in whacking out the No. 4 seed, 6-3, 6-4, 6-2.

Vilas was the only seed beaten - in fact, the only one seriously threatened - on a day when Wimbledon scrambled to get caught up with the schedule after all play was rained out on Thursday.

A few more showers yesterday slowed the recovery process, prompting the abandonment of the traditional 2 p.m. starting time today and Monday. For at least these two days, Referee Fred Hoyles announced, play would commerce "at 12 noon, precisely."

Okker, 34, first played Wimbledon as a junior in 1961. He has been in the men's singles draw 13 times since 1964, reaching the quarterfinals in 1968, '69, and '75, and was seeded ninth as recently as 1976. Last year he lost in the fourth round to Ilie Nastase on Centre Court.

But this year, he had been the low-flying Dutchman. Coming into this week he had won only three singles in 1978, suffering through a dozen first-round defeats as his world ranking on the computer printout of the Association of Tennis Professionals plummeted to No. 104.

The nadir came three weeks ago when he lost to Wouter Fok, ranked only No. 7 in Holland, in a tournament at Mook, in The Netherlands.

"To lose to Fok in Mook, it was a disgrace," said one Dutch journalist on the scene yesterday. "Okker would not talk to us, or to the radio and television. He was very angry, and he got terrible press.Everyone said that he was finished, nothing anymore but a doubles player."

Yesterday "Tiny Tom" - 5-foot-10, 143 pounds, and full of all his old nimbleness and fidgety energy - showed it ain't so.

He sensed early that Vilas, never as comfortable on grass as he is on clay or indoor courts, was off-form and vulnerable. Okker played beautifully from beginning to end, never allowing the ruggedly muscular Argentinian time to dig himself out of his rut. "I was trying to the last ball," Vilas said later, "but I was not there."

Okker has a relatively lightweight serve, but he volleys with clean and agile efficiency. He is particularly good on low volleys, which enabled him to handle Vilas' dipping, heavily topspun service returns. Consequently, he lost only three points on his serve in the first set.

From 3-3, he won 12 points in a row to take the set. In the break game for 5-3, Vilas muffed two volleys and double-faulted for the break after Okker passed him with a stinging backhand.

Okker's streak reached 15 straight points as he got to 0-40 on Vilas' serve in the first game of the second set. Vilas cracked a service winner, but then netted a backhand volley for the break. Okker held at love again: He had won 20 the last of 21 points.

Only once did Vilas look as if he might plug the hole in the dike. He played strong games to break back to 2-2 - Okker netted a forehand volley at 15-40 - and to hold at love for 3-2. In that game Vilas creamed a forehand winner from mid-court and crunched an overhead, an ace and a service winner.

They went on serve to 4-4, but then Okker broke again after three deuces in a game in which Vilas served two more double-faults. The second pushed him to break point, after he had squandered three game points. Okker laced a beautiful backhand down-the-line passing shot off an indecisive forehand volley and served out the set at love.

Vilas lost his serve again in the opening game of the third set, netting a forehand volley and pushing a backhand volley long off solid but unspectacular service returns.

Okker held at 15, had another break point on Vilas' serve then held again at 30 for 3-1. He was stroking the ball confidently, punching his volleys deep, anticipating Vilas' passing shots almost flawlessly, covering Vilas' tendency to go cross-court on the backhand most of the time.

A mist started falling and Okker fell 0-30 down as he served at 3-2, but he recovered and held after one deuce. In the next game a forehand cross-court winner and backhand return winner got him to 30-40, and Vilas double-faulted again to 2-5. Okker served out the match at 15.

He now plays California Tom Leonard, who has served his way through the section of the draw weakened by Arthur Ashe's first-round defeat, for a place in the quarterfinals.

The other top seeds who played yesterday - No. 1 Bjorn Borg, No. 3 Vitas Gerulaitis, and No. 7 Raul Ramirez - all won in straight sets, so did Martina Narratilova, Virginia Wade and Billie Jean King, the Nos. 2, 4, and 5 seeds in the women's singles.

Billy Martin, Vilas' conqueror last year, ousted Erik van Dillen, who had ambushed John McEnroe in the first round, 5-7, 7-5, 6-8, 6-4, 7-5.

Fred McNair IV of Checy Chase, Md., who had to win three qualifying matches to get into the tournament, scored a good win over Peter Fleming, ranked 37th in the world, 9-8, 6-8, 4-6, 8-6, 6-3.

McNair led, 9-8, 4-2, 30-0 on his serve when Fleming managed to swing the momentum of the match, winning the second and third sets and breaking McNair for a 1-0 lead in the fourth.

But McNair broke right back at love, hitting two return winners to 0-30 and benefitting from a Fleming double-fault and volley error. At 6-6, McNair held from 0-30 with four solid first serves and first volley winners.

Then he immediately broke for 7-6 with two forehand winners, an angled backhand passing shot and a volley after taking the net behind a good lob.

McNair broke for 4-2 in the final set and led, 5-2, when the rain came, sending them to the dressing room. When they returned, Fleming won five points in a row, but McNair again reeled off four straight points from 0-30, winning the match point with a good serve to the backhand and a backhand first volley that forced an error.