VISITORS to San Francisco who want to ride "halfway to the stars" on the famed cable cars have only a few more weeks to board the trolleys. On Sept. 22, America's "only national landmark on wheels" will close down for two years so the creaking old system can be repaired.

The city's "Save the Cable Cars" campaign has now raised about $9 million and will definitely reach its $10-million goal to preserve the popular tourist attraction, according to Dale Hess, general manager of the Convention & Visitors Bureau.

It will cost an estimated $58.6 million to overhaul the main power system that runs the winches and fix the tracks and rusted cables under the streets, Hess said. "The cars are in fine shape." The U.S. Department of Transportation's Urban Mass Transportation Administration has agreed to provide 80 percent of the cost if the city raises $10 million (it has already made a $12.5-million grant) -- assuming Congress does not erect a last-minute roadblock.

Most of the funds so far have come from major U.S. corporations, hotels and restaurants, Hess said, but donations have also been received from individuals and small businesses around the country and overseas. An appeal to the general public will wind up the campaign on Sept. 18 with a telethon in San Francisco.

The cars will be back in service in June 1984, Hess said. It was on Aug. 1, 1873, that inventor Andrew Hallidie guided the first cable car down Nob Hill. Today the fleet of 39 cars carries 12 1/2 million passengers a year, more than half tourists. City officials, concerned about the possibility that visitor totals might drop while the trolleys rest, are arranging for double-decker buses to run along some routes "to take up the slack," Hess said.

Seafood lovers will have ample opportunity to whet their appetites at the 16th Maryland Seafood Festival Inc., scheduled to open a three-day run on Friday, Sept. 10, at Sandy Point State Park, which is at the west end of the Chesapeake Bay Bridge just outside Annapolis.

When the event started in 1965, it was called the Clam Festival, but it now includes Maryland's famed blue crabs, shrimp, oysters -- and, of course, clams steamed, fried or in tasty chowder. You'll also find the ubiquitous hotdog, pizza, vegetables and drinks. The seafood dishes will be prepared and served by members of community groups who share the proceeds, according to the Annapolis Chamber of Commerce.

In addition to the food, there will be music, skydiving exhibitions and other events. Hours are 1 to 8 p.m. on Sept. 10, 10 a.m. to 8 p.m. on Sept. 11, and 10 a.m. to 6 p.m. on Sept. 12. Admission is $2.50 for adults, children under 14 free, and includes parking, beach strolling and entertainment -- the food is extra. The festival, a subsidiary of the Chamber of Commerce, drew 28,000 visitors last year.

American Express and First Family of Travel will become the first foreign tour operators to do business in China under an agreement approved this month in Peking, according to the U.S. Travel & Tourism Administration.

Under terms of a "memorandum of understanding" signed by Peter McCoy, under secretary of Commerce, and Han Kehua, director general of the China General Administration for Travel and Tourism, both companies will be permitted "to assist American travelers in China and maintain a relationship with the official Chinese government travel organization," USTTA announced.

The government-owned China International Travel Service opened a New York office last April. New York-based American Express, and First Family of Oakbrook, Ill., are planning to be in full operation in Peking this Fall (American Express has had a representative in Peking since Oct. 1979, who has helped with the company's tours and aided card-members, but the agreement registers the office).

It's doubtful that Marlon Brando designed it himself, but the star's name gets prominent billing on the cover of a slick, full-color travel brochure promoting "Marlon Brando's Private Atoll, TETIAROA."

Hotel Tetiaroa -- as many escapists already know -- is the actor's Tahitian hideway. Brando owns the hotel and the entire atoll. The new brochure (which manages to include a few bare-breasted vahines in the lush South Pacific island scenes) notes:

"Only a 20-minute flight from the hustle and bustle of Papeete... There is peace and quiet. No pollution. Miles of empty white sand beaches... Picnic lunches on a deserted island... A well-stocked bar. Spectacular sunsets. French, Tahitian cuisine." Rate is $60 per person in a shared twin bungalow with private bath and all meals. There are 12 islands in the atoll.

And who knows whom you might run into.