All you had to do was take one look down normally bustling St. Nicholas Ave. in Washington Heights yesterday afternoon to sense an astonishing event was underway.

Around 12:30 p.m., Luis Carillo and Abimael Classen stood in front of their shuttered Chavin Hardware store near the corner of W. 178th St.

"We"re closed to support the immigrant protest," Carillo said, his arms folded serenely under a brilliant sun.

Carillo came here from Peru more than 35 years ago, and has long since become a citizen. He realized his American Dream. Now, it was time to take a stand for those less fortunate, he said.

Virtually every store owner along St. Nicholas made the same decision, even if that meant turning away a few almighty dollars for one day.

The Capri Restaurant on the corner. The Los Primos Fruit Store. The big Bravo Supermarket down the street. The Happy Land Chinese Restaurant.

All were closed yesterday, some for a few hours, most for the entire day.

Over on Broadway, it was the same story.

Yasmin"s Fashion Store. Torres Bakery. Casa Linda Upholstery. Columbia Pharmacy. Angel Shoes. Fort Washington Hardware. Aztek Records. Santa Ana Botanica. Quisqueya Grocery. Fernandez Check Cashing.

All closed.

By the end of the day, thousands of immigrant-owned businesses all over America had pulled off perhaps the biggest one-day boycott this country has ever seen.

Even huge corporations like Tyson Foods and Cargill"s reluctantly closed their factories so their largely immigrant workers could join - of all things - a national May Day demonstration for the legalization of millions of undocumented workers.

And once again those immigrant workers, both legal and illegal, poured into the streets of downtown Manhattan and scores of other cities and towns, their children and baby carriages in tow - in numbers too breathtaking for anyone to ignore.

"No one knows the pain we feel," said Miguel Baez, who came here illegally from Mexico five years ago and works as a bartender in Manhattan.

"We need these jobs to survive," he said. "But we can"t visit our families back home for years for fear we"ll get caught coming back."

It is that endless agony of living in the shadows that has driven so many to join these massive protests.

They march even though they risk being fired or being detained and deported by immigration authorities.

They boycotted schools and jobs and shut down stores yesterday even though Catholic Church officials and union leaders and politicians who support their cause urged them to ignore the call for May Day protests.

They took to the streets even though the pundits and the so-called experts in Washington warned of a political backlash from middle-class America.

Some have even tried to pit black Americans against the undocumented. But key African-American leaders like the Revs. Jesse Jackson and Al Sharpton and Transport Workers Union chief Roger Toussaint all attacked those divisive tactics at yesterday"s Union Square rally.

"You can"t talk about globalized capital and exporting jobs and not talk about global human and labor rights for immigrant workers," Jackson said. "Immigrants aren"t sending good jobs overseas, corporations are."

Time and again this new immigrant movement has taken the politicians, the church and labor leaders by surprise with its discipline and its fury.

The experts, you see, are missing the point.

This movement is already a backlash - against decades of anti-immigrant scapegoating and hysteria in Washington. Congress ignores this cry for recognition at our country"s peril.

Juan Gonzalez is a Daily News columnist. Email to: jgonzalez@edit.nydailynews.com