''YOU couldn't have come at a better time. They just lit the giant Christmas tree on Union Square, which is right across the street from your hotel.''

The slightly hoarse voice of Gus Whitcomb of Cathay Pacific's USA team crackled over the public address system in the bus carrying a group of media visitors from Asia.

He needn't have strained his voice further to say more. I was predisposed to like San Francisco, having been told how lovely it was and how appropriate that it should be my introduction to the US mainland.

The timing of the airline's Hong Kong-San Francisco inaugural flight--when the city, like many others around the world, was dressed up for the holidays--was just perfect. Especially so, because we arrived in the evening when the city was all lit up.

And so, lights created my first images of the city by the bay. Ironically, their absence made the brief visit unforgettable. By a rare coincidence, I and my companions found ourselves right smack in the middle of a massive power failure barely halfway through the trip! But that's a different story altogether.

Long before the bus that fetched us from the airport pulled over on the side of the Westin St. Francis, I had decided that my first tour would be around the block, and my first stop would be Union Square. It was nearly 8 p.m., but my day was just beginning.

A crane, which presumably had hoisted the decorating crew, was still parked by the Christmas tree on the square. Although slightly distracting, it could not diminish the grandeur of the towering structure of infinitesimal lights topped by a string of more lights shaped like a five-point star.

Around the base, keeping the crowds at a safe distance, was a low, steel fence onto which were mounted yet more lights, rectangular flourescents which illuminated a bed of big red and mint-white poinsettias on one side. An elderly couple snuggled beside each other on a bench right in front of the flowers, as though keeping an eye on the tree and its admirers.

Slightly competing with the lights on the square were the brightly lit giant wreath above the entrance of Macy's across the street toward the left. Complementing this centerpiece, like a chorus of carolers blending with the soloist, were rows of smaller versions of the wreath spread out across the entire facade of the store.

Real singing, however, broke out from the square itself, compliments of a trio of impromptu carolers who tried to get promenaders to join them. One of them, a black man, jazzed up ''Hark, the Herald Angels Sing'' a cappella. Midway through, he called out again to passersby.

A Caucasian woman, obviously familiar with this type of street performance, obliged with a few bars, eliciting applause even from strangers.

''Hey, lady, how 'bout you?'' the singer went on.

Who, me? I thought. No way. Although for a fleeting moment, I felt as though all the excitement of the trip had charged me with enough Christmas spirit (or bravura) to go up there and show 'em. After all, who'd ever know that once I tried to revive an aborted singing career on Union Square!

I decided to play safe and walk away, humming the tune to myself.

Drawn by the charming Victorian-type posts, all decked in big, burgundy bows, I circled the block and even ventured down Powell Street on the side of the hotel and up to Market Street. There, near the stairway leading to the underground BART station, a more spirited group of street singer--no, rappers--were cajoling one another, ending up in a mock melee.

This, plus a stranger who suddenly caught up with me with a plea to ''spare some change'' jolted me out of my holiday reverie and sent me heading back to the safety of my hotel. I was not about to live out an episode of Karl Malden's ''Streets of San Francisco.''

The Westin St. Francis quickly restored the holiday mood. Just past the main entrance, which we missed when we entered through a side door earlier, hung a brilliant red banner welcoming guests to the ''World's largest Santa Convention.''

I looked around, thinking it meant a gathering of people who played Santa, only to realize it referred to the displays in the lobby. Santa Claus dolls in different sizes, colors, poses and costumes from all over the world, had overrun the hotel. Some, like the mechanical ones, were set in large glass viewing cases at the lobby lounge. Others were propped on a display ledge above the front desk. Still others dangled from branches of a Christmas tree near the bell desk or adorned wreaths on the walls. And, as we later found out, a couple of chocolate Santas appeared on the night table of every guest room every day.

An added attraction at the lobby was a snow-covered castle-like structure, which turned out to be a baked wonder created by the hotel's pastry chef. Standing about six feet, it was made of gingerbread and marzipan!

In just two hours, I had seen so much. And the tour was to start only the next day.

For the next two-and-a-half days , we would be taken on a whirlwind tour of the city, recently voted ''Top City in the US'' by readers of Conde Nast Traveler magazine for the 10th year, and by readers of Travel & Leisure magazine for the third year. Three San Francisco hotels were also among the top hotels in the world--the Ritz Carlton, Sherman House, and Mandarin Oriental, which hosted our first breakfast in the city in one of its suites offering breathtaking views, plus a mounted gold-plated telescope with which to look at them.

Kicking off the tour was a daylong trip to Napa Valley, where we sampled world-famous sparkling wines from Mumm, Meadowood and the private Harlan Estate. Accompanying us were Laurie Armstrong, vice president for public relations of the San Francisco Convention and Visitors Bureau, and Betty Law and Lavina Chan of Cathay Pacific's head office, who traveled with us from Hong Kong.

The second day would have been more exciting, with a cable car ride to Fisherman's Wharf scheduled. But that was blacked out.

We did have a look-see at the Yerba Buena Gardens, a 12-block area billed as ''San Francisco's newest and most exciting neighborhood.'' Focal point was the Rooftop at Yerba Buena Gardens, built by the San Francisco Redevelopment Agency as an urban destination for the youth and their families.

Opened just last October was Zeum, an art and technology center where kids and their parents can give vent to creative energies and try their hands at visual, media, and performing arts. What the youths create here are exhibited or viewed by the public.

At the Center for the Arts, we viewed offbeat exhibits of bicycles and photos chronicling a police detective's work.

Fortunately, the Alcatraz tour went on as scheduled in the afternoon. But that again is the subject of another story.

Capping the trip was a walking tour of Chinatown, the second most visited by tourists in San Francisco. The tour was conducted by culinary expert and author Shirley Fong-Torres, who carries the Filipino name her father used to get into the US at the time its government restricted the entry of Chinese.

We were back at Yerba Buena Gardens on the evening of our second day for the inaugural gala dinner at the San Francisco Museum of Modern Art. In his speech, Cathay Pacific CEO David Turnbull said San Francisco was the ''natural gateway'' to the US from Hong Kong because of its big Chinese community.

As is the tradition in the airline when launching destinations, he compared Hong Kong and San Francisco. Both had ''splendid harbors, city views, bridges... and traffic,'' he noted. But in addition, Hong Kong has a new airport ''and lots of electricity,'' he quipped, recalling the morning's blackout. Clearly, people were not going to forget easily what happened hours ago.

Even after the tour, the lights of San Francisco still held their spell. On the eve of my return to Manila, I stayed with an aunt, University of San Francisco Prof. Aida Alcala-Joshi, who lives in El Cerrito. From the hills of the suburb across the bay, San Francisco looked like a fantasy land, its lights shining brightly in the clear sky and casting magical images on the waters of the bay.

''You're lucky. This is the first time in several days that we have clear skies,'' she said.