LOS ANGELES, California (AP) -- They surprised the police, and maybe themselves, their T-shirts turning block after block of downtown Los Angeles streets white in a demonstration so massive that few causes in recent U.S. history have matched it.
Police said more than 500,000 people marched Saturday to protest a proposed federal crackdown on illegal immigration.
Wearing white as a sign of peace, and waving flags from the U.S., Mexico, Guatemala and other countries, they came to show that illegal immigrants already are part of the American fabric, and want the chance to be legal, law-abiding citizens. (Watch sea of humanity in L.A. -- 1:47)
Police used helicopters to come up with the crowd estimate. "I've been on the force 38 years and I've never seen a rally this big," said Cmdr. Louis Gray Jr., incident commander for the rally.
In Denver, Colorado, more than 50,000 people protested downtown Saturday, according to police who had expected only a few thousand. Phoenix was similarly surprised Friday when an estimated 20,000 people gathered for one of the biggest demonstrations in city history, and more than 10,000 marched in Milwaukee on Thursday.
The demonstrators oppose legislation passed by the U.S. House that would make it a felony to be in the U.S. illegally. It also would impose new penalties on employers who hire illegal immigrants, require churches to check the legal status of parishioners before helping them and erect fences along one-third of the U.S.-Mexican border.
"I think it's just inhumane," said Elger Aloy of Riverside, a 26-year-old premed student who was pushing his 8-month-old son in a stroller at the Los Angeles march. "Everybody deserves the right to a better life."
Many demonstrators said they had immigrant relatives or had crossed the border themselves.
"My mom came from Mexico. She had to cross the river, and thank God she did," said David Gonzalez, 22, who held a sign saying, "I'm in my homeland."'
Gonzalez rejected claims by advocates of the legislation that it would help protect the nation from terrorism, noting that it would hurt Hispanics the most.
"When did you ever see a Mexican blow up the World Trade Center?" he said. "Who do you think built the World Trade Center?"
The Senate was to begin debating immigration proposals Tuesday.
President Bush is pushing for a guest worker program that could provide temporary legal status for some of the estimated 12 million undocumented immigrants in the United States, but many of his fellow Republicans are taking a more restrictive stance.
"As we debate the immigration issue, we must remember there are hardworking individuals, doing jobs that Americans will not do, who are contributing to the economic vitality of our country," Bush said Saturday in his weekly radio address.
Some immigrant-rights advocates, however, are also against Bush's proposed guest worker program, saying it would create an underclass of foreign workers.
Illegal immigrants want legislation that would protect them, unify their families and address future flows of immigrants, Lisa Duran, of the group Rights for All People, said at the Denver protest.
The rally at Denver's Civic Center Park, like the one in Los Angeles, was peaceful. Denver police spokesman Sonny Jackson said the crowd, mostly made up of families and older people, was respectful.
Arvada resident Elsa Rodriguez, a pilot who came to Colorado in 1999 from Mexico to look for work, said she came to the Denver protest because she just wants to be considered equal.
"We're like the ancestors who started this country. They came from other countries without documents, too," said Rodriguez, 30. "They call us lazy and dirty, but we just want to come to work. If you see, we have families, too."