WASHINGTON — Thousands of immigrants came to Capitol Hill on Tuesday for a day of lobbying and an afternoon rally calling for comprehensive immigration reform.

The event was timed to the unveiling of an immigration bill by Representative Luis V. Gutierrez, Democrat of Illinois and chairman of the Immigration Task Force of the Congressional Hispanic Caucus.

With President Obama’s stated commitment to immigration reform, advocates for immigrants said they hoped to revive a debate that has been overshadowed by other priorities, like the economy and the wars in Afghanistan and Iraq. As deportations continue to rise, immigration reform is needed now, they said, to allow illegal immigrants to obtain legal status and to stop families from being torn apart.

“We need a bill that says if you come here to hurt our communities, we will not support you; but if you are here to work hard and to make a better life for your family, you will have the opportunity to earn your citizenship,” Mr. Gutierrez said in a prepared statement. “We need a law that says it is un-American for a mother to be torn from her child, and it is unacceptable to undermine our work force by driving the most vulnerable among us further into the shadows.”

Immigration overhaul faces a difficult road. President George W. Bush twice failed to get Congress to pass similar legislation. Mr. Obama recently said his administration would pursue reform this year but expected no action on legislation before 2010.

Tuesday’s event was sponsored by various immigrant advocacy groups, including the Reform Immigration for America campaign, the National Capital Immigration Coalition and Families United/Familias Unidas. It attracted convoys of buses, vans and cars carrying more than 3,000 demonstrators from at least 17 states.

Immigrants, religious leaders, members of Congress and immigrant advocates planned to gather on the West Lawn for speeches and a prayer vigil at 3 p.m. Similar rallies were being held in at least 20 cities around the nation, including Los Angeles, Milwaukee, Denver and Albany.

“I’m here representing the undocumented workers who cleaned ground zero and its surrounding area after the 9/11 terrorist attacks,” said Rubiela Arias, 43, an illegal immigrant from Colombia who came to Washington with an immigrant advocacy group called Make the Road New York.

Ms. Arias described how she came from Medellín to New York in 1998 with her 5-year-old son, seeking a safer place for her family.

“I worked for eight months cleaning the dust and debris surrounding the World Trade Center,” said Ms. Arias, who cleans offices in Manhattan and was dressed in a light-blue T-shirt with a sticker reading, “Reform Immigration for America.” “There was no question about immigration status. We were all New Yorkers; we were all Americans.”

In June, Senator Charles E. Schumer, Democrat of New York, announced what he called seven principles that would give form to his own reform proposal. Among them were the need to “curtail future illegal immigration,” to have “operational control of our borders” and a “biometric-based employer verification system.” Mr. Schumer, who has been working with Senator Lindsey Graham, Republican of South Carolina, said he would introduce a bill by Labor Day but missed that deadline.

Mr. Gutierrez’s bill, which is likely to propose less restrictive terms than Mr. Schumer’s plan for allowing illegal immigrants to become citizens, is partly meant to pressure his Congressional colleagues.

A main purpose of the rally was to highlight the way current immigration law splits families.

“Families deserve better than this from our government,” said Peter Derezinski, a 17-year-old high school senior and a United States citizen whose father was deported to Poland in April 2008 after 18 years as a truck driver and an air-conditioning repairman in Chicago. “We need to fix our broken immigration system so our parents who have contributed to this nation’s economy in a positive way have a chance of reuniting with their children.”

Robin Ferschke, who was traveling from Maryville, Tenn., said she planned to talk to lawmakers about changing the law so that her daughter-in-law and grandson could live legally in the United States. Ms. Ferschke’s son, Sgt. Michael Ferschke, a 22-year-old Marine radio operator, was killed in Iraq in 2008, leaving his Japanese widow and their infant son in immigration limbo.

While Sergeant Ferschke was deployed to Iraq, he learned that his girlfriend was pregnant. They decided to get married by proxy, a method that has a long history in the military when the bride and groom cannot be in the same place for a ceremony. The boy was born in Japan and holds dual citizenship.

But under a 1950s legal standard meant to curb marriage fraud, the wedding is not recognized for immigration purposes even though the military recognizes the union.

“The laws we have now are inhumane and need to be changed,” Ms. Ferschke said. “So I came to beg lawmakers to change that and not force my daughter-in-law and my grandson to leave the country.”