Forgotten War : Filmmaker will retell details of the U.S.-Mexican battle fought locally.

When Paul Espinosa explains his new film project, “The U.S.-Mexican War (1846-48),” excerpts of which will be shown at the Autry Museum of Western Heritage on Saturday, he plans to be direct.

“There was a war that happened here,” the San Diego-based public-TV veteran will tell California children and parents attending his lecture on the making of his documentary.

Even though he’s talking about a part of history kids learned about in the fourth grade--when they studied California history--hardly anyone, including adults, is aware that statehood was preceded by a two-year shooting war with Mexico.

Espinosa’s film reveals that the final volleys were exchanged along the banks of the Los Angeles River, and the cease-fire took place at the spot where the Universal Studios tour now operates.

That was 150 years ago, and memories north of the international border created by the war have faded. But not to the south. In the course of his three years’ work on the film, Espinosa said he noticed, “When I talked to Americans, they had never heard of it--it was a blank. But Mexicans today have no trouble recalling it.”

This dichotomy will be discussed during Espinosa’s behind-the-scenes explanation of the making of the film. “This is the first time that historians from both countries have collaborated on such a project,” said Espinosa.

And judging by on-screen comments of Mexican historians interviewed for the show, it appears that emotions still run deep.

The film is full of live-action battles re-created for the TV camera. It also contains stills from the period--unique because this was America’s first war to be photographed. Some girls may notice that Ulysses Grant, who got into the fighting right after graduating West Point, was rather dashing as a young man.

The film doesn’t--nor do the actual facts of the war--add up to a story where one side (the U.S.) was beastly while the other side (Mexico) behaved well. Each side in the U.S.-Mexican War nearly collapsed into a civil war. Around Los Angeles, many Mexicans fought on the side of the U.S.

Mexico toppled its own president and then suspected the new one of working for the Americans. Thousands of American soldiers deserted during the fighting. Hundreds of these American deserters were so angry at their country that they joined the Mexican Army and became national heroes in Mexico, defending that nation’s capital against U.S. invaders.

BE THERE

“The Making of the Documentary: ‘The U.S.-Mexican War,’ ” Saturday, 2 p.m., at Autry Museum of Western Heritage, Wells Fargo Theater, 4700 Western Heritage Way, Los Angeles. Admission: museum members $4, nonmembers $5. (213) 667-2000.

The entire film will be aired in twoparts on PBS Sept. 13 and 14.