Panic gripped South Florida's undocumented immigrant communities as rumors spread throughout the nation that immigration agents were conducting random raids -- detaining people on the streets, in stores, restaurants and shopping malls.

From Homestead to Key Biscayne and Aventura -- and from Pembroke Pines to Lake Worth -- potentially thousands of undocumented immigrants are staying home this week. Many fear venturing onto the streets lest they wind up deported, even though no evidence surfaced of widespread sweeps.

Business managers throughout South Florida said they saw a dramatic drop in the number of immigrant workers showing up at work sites since Monday. In Homestead, where anywhere from 200 to 300 workers wait on a street corner near Krome Avenue most every morning to be picked up by employers, only a couple dozen were spotted Tuesday.

Mario, an undocumented Guatemalan in Homestead who would not give his last name, said he was afraid to go out since reports of immigration raids began over the weekend.

''I try to go find work in the morning and then go straight home after I finish working,'' he said. ``Before, I'd go and do some shopping or get together with friends after work.''

Dan Shaw, president and chief executive officer of Associated Builders and Contractors in Coconut Creek, said more than 100 immigrant construction workers had left work sites in Broward and other parts of South Florida and not returned since rumors began.

''This scared off immigrants at multiple work sites,'' Shaw said.

But even though immigration agents conduct operations, and detain foreign nationals every day, they generally go after people wanted for crimes or those who have evaded deportation orders. Immigration authorities insisted they do not engage in random raids.

In fact, there was no evidence that any of the raids people called The Miami Herald about over the last three days actually happened.

The rumors appeared to be just that.

Nevertheless, they spread alarm through South Florida's tense immigrant communities -- just days before planned marches and rallies, and a proposed immigrant work stoppage on Monday, as part of International Workers Day.

Some immigrant rights activists worried that the loud, national debate over undocumented workers' future had left many nervous and easily spooked.

Opponents, they suggested, could be spreading rumors of raids just to scare workers away from political events.

''I honestly think it's psychological warfare in retaliation against immigrants in anticipation of the May 1 protests,'' said Jonathan Fried of WeCount! in Homestead.

Raid rumors were not limited to South Florida.

Homeland Security officials said they were flooded with telephone calls around the country from the media and the public about the alleged random raids by U.S. Immigration and Customs Enforcement agents.

''ICE agents conduct operations every single day in locations around the country,'' said Jamie Zuieback, an ICE spokeswoman in Washington. ``Operations are not random sweeps, but carefully planned enforcement actions that result from investigative leads and intelligence.''

U.S. officials said they believe the rumors started after Homeland Security Secretary Michael Chertoff last week announced a crackdown against employers who hire undocumented foreign workers.

Chertoff's announcement came coupled with the disclosure that ICE agents detained 1,187 unauthorized immigrants in 26 states, including 38 in Tampa.

Then on Monday, ICE officials in Miami announced the biggest sweep of criminal and undocumented immigrants in Florida in a decade.

A total of 183 people, including 43 convicted criminals, were detained in the Miami area and three other cities.

Most of the migrants, 130, had evaded deportation orders -- but another 53 were detained because they were nearby when immigration officials found the alleged absconders.