LAMPEDUSA, Italy >> Until a few weeks ago, the immigrant transfer center on this tiny Mediterranean island — a kind of Italian Ellis Island — was empty. An extensive European campaign against migration from Africa was considered so effective that the authorities basically shut it down.

But since the Tunisian government collapsed in January, spurring unrest across North Africa, Lampedusa has been bustling. The Italian police tow in boats full of desperate immigrants — about 6,000 refugees in the past two months. Young men in hooded jackets smoke cigarettes and await transfer to the mainland — a prospect that is striking fear in many European hearts.

The turmoil in Libya and elsewhere in the region has toppled or undermined North African dictators who negotiated a web of benefits from Europe, including aid and diplomatic standing, in return for stopping immigrants seeking to cross the Mediterranean.

Without the assistance of those leaders, many in Europe worry that they will face new waves of illegal immigration not only from the liberated areas in the north but from much of sub-Saharan Africa as well.

The immigrants would arrive at a time when much of Europe — struggling with high unemployment and lethargic economies — is already awash with anti-immigrant sentiment, and many countries say they are simply incapable of absorbing poor migrants.

“In Italy, there is really a panic,” said Anna Triandafyllidou, a migration expert with the Hellenic Foundation for European and Foreign Policy. “Everything is up in the air and no one knows what to do.”

Unable to build the kind of border fence that the United States has erected to keep Mexicans at home, countries like Spain and Italy have spent years forging close relationships with North African leaders, persuading them to prevent migrants from trying to sail the rough seas of the Mediterranean. In return, Morocco, Tunisia and particularly Libya sometimes used brutal tactics to keep immigrants from ever getting near European shores, human rights activists say.

Italy’s agreement with Libya, signed in 2008, was considered especially effective. Italy pledged $5 billion over 20 years in exchange for Libya blocking would-be immigrants from leaving. Almost overnight immigrants stopped arriving in Lampedusa.

According to the Italian Interior Ministry, in 2008, more than 36,000 immigrants came ashore in Italy — not only from North Africa but from the Horn of Africa, Niger and Nigeria. After the treaty, that number dropped to 9,500 in 2009 and slowed to a relative trickle in Lampedusa.

Now, the island’s local population of 6,000 is once again outnumbered by detained migrants, according to the ministry. At 3 a.m. Wednesday, an Italian police boat arrived with 55 tired and shivering immigrants who had been pulled from a rickety boat. Many were wrapped in thermal blankets. One was taken away on a stretcher.

At one point, there were so many immigrants here that the authorities allowed them to wander the island freely rather than keep them locked up. Inside the center Wednesday, hundreds of young men, almost all from Tunisia, were eager to tell visitors their message: “We want work.”

“I got a high school degree, I worked fixing cars, but there’s no work,” said Mander Grebis, 25, in halting French, as he stood in a group of young men huddled in front of the center’s one vending machine.

He and the others said they wanted to stay in Italy or to go to France to find jobs.

Italy’s arrangement with Libya was hardly the only one. Spain, too, has over the years enlisted the help of Morocco and other African countries in dealing with immigrants. Experts say it has offered countries equipment for patrolling shore lines and economic aid of all sorts — so that immigrants have fewer reasons to leave and African governments have more reason to help.

Spain offered Senegal money to help repatriate immigrants who were often returned to the Dakar airport but did not have the money or the incentive to return to their villages. At times, the European Union pays for such projects, too.

But human rights advocates say some of these arrangements have abetted the harsh treatment of immigrants, particularly in Libya. In a report published in 2009, Human Rights Watch said migrants who eventually made it to Malta and Italy described being beaten and robbed of valuables and their documents while in detention in Libya.

The report also said electric shock batons were used to force migrants off the boats in Libya. And some said they were handed back to traffickers who held them for ransom.

“These agreements,” said Bill Frelick, the author of the report, “are with partner states that often don’t have the same standards as Europe. They often treat migrants in humiliating and denigrating ways.”

In an interview, Sen. Lamberto Dini, a former Italian prime minister who helped negotiate Italy’s treaty with Libya, said such reports had “not been proven.”

There have also been disturbing episodes in Morocco. In 2005, 11,000 sub-Saharan Africans who had been stranded in Morocco after a renewal of Spanish-Moroccan partnership, stormed the border fence surrounding the Spanish enclave of Melilla, on the African coast. Some made it across, but several were shot dead and some of the immigrants who were eventually turned over to the Moroccan police were then dumped into the Sahara.

But the agreements have been effective.

In the past year, control of the African coastline was so tight that immigrants were turning to a wholly different route, showing up on the land border between Greece and Turkey. In recent weeks, Italian officials have warned of a “biblical exodus” in which as many as 300,000 could arrive, though many experts say that number is intended more as a way to stir up passions domestically than as a reflection of any clear reality.

Experts say any number is conjecture given the fluidity of the situation in North Africa and the difficulties involved in distinguishing the number of workers trying to return home from the refugees trying to flee.

In the Lampedusa, the immigrants stay for two days before being sent to mainland Italy for more processing to determine if they are seeking political asylum or are instead “economic immigrants” seeking work.

Over the years, aided by sometimes alarmist press coverage of immigrants arriving on boats, Lampedusa has taken hold in the Italian and European popular imagination as the image of out-of-control immigration. In a sign of how crucial Lampedusa has become to that image, especially for some right-wing parties, Marine Le Pen, president of France’s far-right National Front, plans to visit the island on Monday.

Tommaso Della Longa, a spokesman for the Italian Red Cross on Lampedusa, said the organization was setting up a field hospital on the dock in Lampedusa to provide emergency medical aid for immigrants who arrived after long, rough crossings.

“It’s better to be prepared,” Della Longa said, “if — and I underline if — the thousands of immigrants that people are talking about arrive.”

© 2011 The New York Times Company