Americans again demonstrated their continuing fascination with Richard M. Nixon when more than 8,000 persons flocked here yesterday to tour the grounds of La Casa Pacifica, the seaside villa that is home to the former president.

"This is bigger than King Tut," exulted Alex W. Goodman, executive manager of the San Clemente Chamber of commerce which sponsored the bus tour.

Goodman said that most of the $20,000 the chamber raised at $2.50 a tour ticket was spent on a party Saturday night celebrating the 50th anniversary of this peaceful resort and retirement community located midway between Los Angeles and San Diego. The party featured a 47-foot birthday cake ("Nixon was supposed to pop out of it," joked a resident) and a rendition by Metropolitan Opera singer William Olvis of the local hit, "On the Beach at San Clemente."

Most of those who came to see La Casa Pacifica ("House of Peace") and the adjacent buildings which President Nixon had called the "Western White House" were elderly persons, some from retirement communities 200 miles away. Many were outspoken Nixon supporters who mingled with curious sightseers, camera buffs and two busloads of reporters.

"I'm a great believer in Nixon," said 77-year-old robert Pennington of Rancho Bernardo. "I have terrific respect for him and I think he was butchered."

Clifford Reed of San Dimas recalled proudly how he had voted for Nixon four times, and his wife Dorothy added: "I think they should impeach Carter because he's not doing a good job."

But there were some in San Clemente who were indifferent to the event and a few who expressed hostility.

Dr. Marvin Colter, playing racquet ball with his 10-year-old son Avery at the high school where the tour started, shook his head and said of Nixon, "he's just a crook, just a crook."

"But if you give anyone a show for nothing or for cheap, they'll come. It's just something to do on a dull, cloudy day," Colter said.

While most of the people here today seemed sympathetic toward Nixon, many were critical of the brevity of the bus tour.

Buses left in groups of three every 10 minutes on a 20-minute tour that included 10 minutes inside the gates surrounding La Casa Pacifica and the Nixon offices, and five or six minutes on the grounds of the house itself. Secret Service agents and local police rode on each bus and ordered sightseers not to open the tinted windows. Some tourists with cameras complained that this hindered picture-taking.

Judy Yamasaki, 24, of La Mesa, summed up the view of those who thought the tour promised much but delivered little.

"I'm still a supporter (of Nixon)," she said. "The man had a problem, that's all. So does this tour. People are coming from all over the place and you can't see much more from the bus than you can from the highway."

The bus travelers had one advantage over the highway onlookers -- a brief, taped history of the house, which chamber officials said was prepared with the help of Pat Nixon. The commentary included a plea for additional office help to sort the 2 1/2 million letters that have gone unanswered since Nixon's resignation on Aug. 9, 1974.

It ended with these words: "History has been made here. You as the members of the first tour of the grounds of La Casa Pacifica have also become part of history. Hasta la vista!"

Visitors received an autographed, postcard-sized picture of the Nixons, but the former president personally was nowhere in sight. The taped commentary said he was inside the house working on his soon-to-be-published book.

The tour was the brainstorm of San Clemente Mayor Donna Wilkinson, a Nixon supporter who was enthusiastic about the response. She said that one New Orleans couple claimed to have been offered $1,500 back home for their pair of tickets which they declined to sell.

The local and national press covered the event by land and air. One television network persuaded the United Methodist Church to cancel its Sunday services so that the church parking lot could be used as a helicopter landing pad.

While the rest of the town went about its business and surfers tried out the medium-sized waves, the tour proceeded in a brisk and orderly fashion from the San Clemente High School five miles from the Nixon home. Newspaper boys hawked a special commemorative issue of the San Clemente Daily Sun-Post, which was devoted entirely to the anniversary celebration and the Nixons.

One feature in the edition was a series of "frequently asked" questions about the Nixons, including a question about whether Nixon ever had participated in San Clemente civic affairs.

The newspaper's answer: "Not really. Being president is a busy job." CAPTION: Picture 1, La Casa Pacifica and grounds as seen through the tinted windows of a town bus, Tickets for seats were $2.50 each, AP; Picture 2, San clemente plain clothes policeman checks purse under tight security, AP.