On this spot in 1847, the United States acquired a coastline looking toward Asia.

Rain thundered down on the red-tiled roof of “the most important historic landmark west of the Mississippi” as the white boys from San Gabriel, in Indian feathers and bells, stomped and jingled in a cramped circle in the little house.

The dancers, Boy Scouts from the Tatanka Lodge, danced with their adult leaders, including a balding man who wore Indian regalia over what appeared to be old-fashioned red-flannel underwear.

The dancers, re-creating the rites of another culture, had turned out to add their talents to a small celebration of a momentous occasion.

On this spot on Jan. 13, 1847, the United States--a collection of British colonies clinging to the Atlantic Coast fewer than 75 years earlier--became a continental power, spanning North America and acquiring a coastline looking out across the Pacific toward Asia.

It was here, on Lankershim Boulevard just north of the Hollywood Freeway, that the last battles of the Mexican-American War in California came to an end when Gen. Andres Pico, leader of the Mexican forces, surrendered to Lt. Col. John C. Fremont, commanding the California Volunteers.

With the signing of the Capitulation of Cahuenga, California effectively became part of the United States. “The most historic landmark west of the Mississippi” the Campo de Cahuenga site is called in a pamphlet written for the Los Angeles Recreation and Parks Department, which owns it.

Pico’s men, based at the San Fernando Mission, were caught between Fremont’s army of about 300 men, marching down from Northern California, and an American force that had just recaptured Los Angeles, which was then a pueblo occupying a small part of today’s downtown.

The Mexicans had had their day. Using deadly lances and their skill as horsemen, they had earlier won the battle of San Pasqual, north of San Diego, killing 21 and wounding 18 of a 300-man American force that had crossed the continent in an epic march from Kansas, guided in the latter stages by Kit Carson. The Mexicans seemed near victory when they drove American forces out of Los Angeles.

But the retreating Americans had just boarded a ship in San Pedro, ready to abandon the town, when reinforcements sailed into the harbor from Northern California. The two groups joined and fought their way back into the pueblo.

Pico, who had moved north to block Fremont, opted to surrender to him instead of the commander of the force in Los Angeles, Commodore Robert F. Stockton, an American Navy officer who had threatened severe punishment for some of his opponents.

Fremont, making a three-day march across the San Fernando Valley, let it be known that he would offer good terms. Basically, he allowed the Mexican troops to give up their few cannons, go home and be considered U. S. citizens if they wished.

Each year since 1950, when the site--identified long after the war by Fremont, on a visit to California--became a city park, the Campo de Cahuenga Assn. has sponsored a memorial service.

The group, which has dwindled to fewer than a half-dozen members, this year managed to attract about 35 spectators, most of them elderly, to its modest pageant. The whole group would have fit into the back few rows of one of the 150-passenger trams carrying tourists around Universal Studios, whose dark glass office towers across the street loom over the little Spanish Colonial-style building.

L. R. (Bud) Utter, supervising district deputy grand president of the Native Sons of the Golden West, gave a welcoming speech. A color guard from the North Hollywood Law Enforcement Explorer Scout Post, snappy in white gloves and carrying fake rifles of white-painted wood, brought in the U. S. and California flags.

About a dozen Boy Scouts, many wearing Indian-style breech cloths and breastplates over modern clothes, danced to represent the first of the human cultures to pass over the site.

Enrico Estarza, 18, in a black suit, frilly white shirt and red sash--much like the outfit worn by Pico in a gilt-framed portrait looking down on the room--played flamenco guitar to represent Spain and Mexico. His hands flew through a rippling bulerias, drawing shouts of “ole.”

The arrival of American power and culture was symbolized by Chuck Ryan, advertised as “the all-American cowboy and golden voice of the rangeland.” Ryan, 74, who appeared in old Western movies with Hoot Gibson and wrote the song “Cowboy Santa Claus,” launched into “Sons of the Western Soil” before his backup guitarist and banjo player were quite ready.

He apologized, saying he doesn’t actually perform much anymore. But he still packs a mean yodel, as he proved on “When the Sun Sinks Over Sunny California.”

Guy Weddington McCreary gave a short lecture on the historical background of the surrender, comparing Fremont’s services to President James K. Polk with those of Lt. Col. Oliver North to President Reagan. Fremont came to California intending to incorporate it into the United States, McCreary said. “He had to deny what he was really doing, but he knew what the President wanted.”

The Treaty of Guadalupe Hidalgo, which officially ended the Mexican-American War in February, 1848, somehow got the better public-relations treatment, McCreary lamented.

“But this is where it happened, this is where the United States got the land that stretched it from the Atlantic to the Pacific.”