April 10 (Bloomberg) -- Protesters waving American flags and shouting support for looser immigration laws took to U.S. streets by the hundreds of thousands today, keeping the heat on representatives who will reconsider the issue in two weeks.

The marches, coupled with scattered business boycotts designed to demonstrate immigrant economic power, blocked traffic for blocks in cities ranging from Atlanta, Philadelphia, and Garden City, Kansas, to San Francisco.

The National Capital Immigrant Coalition of Washington, an organizer of the marches, said on its Web site the protests were to pressure Congress for citizenship for an estimated 11 million people, plus workplace and civil rights protections. ``Si, se puede'' (``Yes, we can'') was the rallying cry in Washington, San Francisco and elsewhere.

``We're not criminal people. We help this country, and they can help us,'' said Victor Medina, 32, of Silver Spring, Maryland, who attended the Washington rally with his wife after they finished work. ``We need jobs, more opportunities.''

Medina, who delivers Yellow Book phone books, said he moved to the U.S. from Mexico 13 years ago and his six children were born here.

Families in White

Orderly crowds, composed mostly of family groups, spread over the Washington Mall from the National Air and Space Museum, near the U.S. Capitol building, to the Hirshhorn Museum a half- mile in the direction of the Washington Monument. Police directed pedestrian traffic that streamed in from throughout the city and the suburbs.

Hundreds of thousands of participants on the Mall, many clad in red, white, and blue clothing, held homemade signs that read ``We Are America'' and ``We Just Want to Work.'' Organizers onstage near the Capitol led the crowd in several rounds of the Pledge of Allegiance.

At least three-quarters of marchers in the nation's capital wore white shirts that one participant said symbolized peace. Organizers and reporters estimated the crowd as about 500,000. Many carried American flags of all sizes.

Crowds 20 deep stretched a half-mile in lower Manhattan as the New York City rally began. An estimated 50,000 people rallied in Atlanta and an estimated 25,000 turned out in Phoenix, according to the Associated Press.

San Francisco Marches

Crowds at the first of two San Francisco rallies were scattered by heavy rains in the morning. Well over a thousand gathered after work for the second event in the Mission district, long known as the city's Hispanic heartland. Native San Franciscans joined with recent immigrants to express support for looser immigration laws.

Bill Sorro, a native San Franciscan in his 50s whose parents immigrated from the Philippines, said he was glad to ``see our country saying `no' to scapegoating.''

Half a dozen politicians and civic leaders spoke before the crowd to kick off the second march.

``They're going after our children, relatives, classmates, neighbors, and we will not tolerate it anymore,'' said State Assemblyman Leland Yee, who represents the 12th District, which includes San Francisco and San Mateo counties.

``Amnesty for everyone,'' said Lee, who moved to San Francisco from China at the age of three.

`People Feel Strongly'

President George W. Bush called the Washington demonstration a signal that ``this is an important issue that people feel strongly about.'' Bush, who supports a guest-worker program, added that the march was a sign of a healthy democracy.

``We need to understand that we're a nation of immigrants, that we ought to be compassionate about this debate,'' Bush said in response to a question from the audience during an appearance at Johns Hopkins University's School of Advanced International Studies in Washington.

Gustavo Torres, executive director of CASA of Maryland Inc., which backs efforts to allow illegal immigrants to work toward legal status, said the political battle will continue beyond today's demonstrations.

``We are going to keep fighting,'' Torres said, echoing the civil rights movement of the 1960s. ``We are going to register thousands and thousands of people to vote.''

Workers Absent

Among businesses affected by the protests were a few Tyson Foods Inc. plants with absenteeism that was higher than normal as workers attended immigration rallies, company spokesman Gary Mickelson said in an interview. He said fewer than 10 of the Springdale, Arkansas-based company's 100 plants were closed, and added that conditions in the livestock and poultry markets also played a role.

Swift & Co., the third-largest U.S. beef and pork producer, closed a beef plant in Omaha, Nebraska, partly because of anticipated absences for the demonstrations, said spokesman Sean McHugh. He said the Greeley, Colorado-based company's production overall was not affected.

On Sunday, more than half a million people turned out for protests in Dallas, Miami and other cities in 10 states. Today's schedule of 136 rallies was ``the main event,'' said Avril Smith of the Service Employees International Union, one of several supporting the National Day of Action for Immigrant Justice.

Lawmakers Divided

The debate on immigration has divided Republicans, including Colorado Representative Tom Tancredo, head of the Immigration Reform Caucus, who wants to focus on border security and enforcement, and those including President Bush, who back a new guest-worker program.

Last week, a compromise plan for an immigration measure unraveled. Legislation permitting 325,000 guest workers a year and providing a way for an estimated 11 million undocumented immigrants to gain legal status stalled in the Senate.

Republicans and Democrats disagreed on amendments to the measure and how it would be reconciled with a version approved earlier by the House. Last year, the House passed legislation to build 700 miles of fencing along the U.S-Mexican border, and to require employers to verify their workers are legal immigrants.

Senate Judiciary Committee Chairman Arlen Specter, a Pennsylvania Republican whose office in Pittsburgh was the focus of a protest today, said immigration legislation will be his priority when lawmakers return to Washington in two weeks. Specter favors the compromise.

Nation of Immigrants

As of March 2004, about 13.9 million people in the U.S. were illegal immigrants or lived in homes in which the head of the household or a spouse was an illegal immigrant, according to the Pew Hispanic Center in Washington. Undocumented workers made up about 4.3 percent of the civilian workforce, or about 6.3 million workers out of 146 million, according to the Pew report.

In New York City, more than 40 percent of the population is foreign born, according to the Department of City Planning.

Without a fence across the entire U.S.-Mexico border or beefed-up enforcement against employers who hire illegal workers, immigration-policy changes will have little effect on the labor market, said economist Marc Levinson at JPMorgan Chase & Co. in New York.

Wages are depressed because of the large pool of low-skilled workers, and that won't change simply because they are made legal, he said.

``A lot of the policy discussion seems to assume that once this bill is passed, some of the undocumented aliens will simply leave the country and others will stop coming,'' Levinson said in an interview. Those assumptions aren't based on reality, he said.

Mexicans working in the U.S. sent home about $20 billion in 2005, according to the Bank of Mexico, or about 11 percent of the country's 2005 revenue.

Motivated Voters

With candidates already positioning themselves for the 2008 presidential election, one expert said the issue would motivate Hispanics more than to whites.

Larry Sabato, director of the University of Virginia's Center for Politics, said Bush was helped in his two elections by capturing about 40 percent of the Hispanic vote. While the issue may fuel anti-immigration sentiment among some white voters, most won't cast their votes based on it, he said.

``Whereas for Hispanics and Latinos, it's a more central issue and it will probably produce a larger vote shift,'' Sabato said.

Sabato said Republicans' biggest fear is that the immigration issue will chip away at gains Bush made with Hispanic voters.

``That would be devastating simply because without 40 percent of the Hispanic vote, the Republicans can't win the presidency,'' Sabato said.

The issue will have less impact in this year's mid-term elections, which will decide who controls Congress, because there aren't enough competitive races that have large blocs of Hispanic voters, he said.

To contact the reporter for this story: Shannon D. Harrington in New York at sharrington6@bloomberg.net.

Last Updated: April 10, 2006 21:27 EDT