By Steve Scherer

CASALE DI SAN NICOLA, Italy (Reuters) - Migrants arriving at a new shelter outside Rome needed riot police to protect them from far-right activists and furious residents. In the north, locals vandalized a home to keep asylum seekers from moving in.

Traditionally a nation of emigrants, Italy is now struggling to absorb a ceaseless influx of immigrants from Africa and the Middle East. Prime Minister Matteo Renzi is under pressure to stem the flow and his government is fighting to calm tensions.

Migrant arrivals have already exceeded 85,000 this year, following 170,000 in all of 2014. While many of the newcomers look to move swiftly to wealthier northern Europe, some 85,000 are housed in Italian shelters - up from 60,000 last year.

To relieve pressure on Italy's southern regions, where immigrants are initially brought after being plucked from the Mediterranean, the government is seeking to disperse them more evenly in central and northern Italy.

This policy is bringing poor migrants to the doorsteps of isolated or affluent communities, such as Casale di San Nicola, where 250 families live in villas along a private road in the countryside near Rome.

Residents there, flanked by members of the far-right CasaPound movement, staked out the road to keep migrants from occupying the new center for three months before the standoff came to a head in last week's clash. Twenty people were injured.

"We haven't seen an uncontrolled exodus like this since the discovery of the Americas," said Luciano Lupi, 77, a retired marketing manager who lives near the new migrant center. He took a blow to the ear in the scuffles.

"Italy is leaving the door wide open."

Not a day goes by without reports on the Italian news of rescues, shipwrecks, drownings or crimes by immigrants. EU solidarity has been limited - this week the European Union failed to agree to divvy up 40,000 asylum seekers in Greece in Italy among its members.

That has left Renzi's centre-left government vulnerable in the face of a complex international problem that has become a domestic political soccer.

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The Northern League party's firebrand leader Matteo Salvini uses the migrant crisis as a springboard to attack Renzi for not sending home economic migrants who are not protected by international law like asylum seekers.

This uncompromising strategy has helped turned the League - a party traditionally rooted in the north - into the country's third-most popular after Renzi's Democratic Party (PD) and the anti-establishment 5-Star Movement.

The League would garner more than 15 percent in a national vote if a election were held today, according to polls, against 6 percent in last year's European Parliament ballot.

On the other hand, backing for Renzi's PD has dropped over the past year from just over 40 percent to 32-33 percent today, polls show, with immigration partly to blame for its decline.

"The real problem is that 60 percent of Italians think that more immigration equals less safety," said Alessandra Ghisleri, the chief pollster for Euromedia Research in Milan.

"The League takes advantage of this issue because it knows people are afraid."

"AFRICANISATION"

Highlighting the friction, residents in the northern town of Quinto di Treviso last week raided neighboring apartments where about 100 migrants were housed, throwing furniture and mattresses into the street and setting them on fire.

Luca Zaia, the Northern League governor of the region that includes Quinto, has joined two other northern governors in urging mayors to resist the government's efforts to open new migrant shelters in their cities.

While warning of an "Africanisation" of the territory, Zaia successfully negotiated with a government representative to move the migrants out of the apartments and into army barracks.

The Interior Ministry has since announced it will replace the representative, unhappy with her handling of the issue.

Despite such protests, the government is holding to its plan to open shelters across the country, and Renzi has appealed to the values of his centre-left and Catholic base, which has generally supported sea-rescue efforts on moral grounds.

Instead of rightist opponents, "our real adversary is fear," Renzi told a PD assembly on Saturday.

Renzi spoke after a 10-year-old diabetic girl from Syria died at sea because smugglers had allegedly ditched her insulin.

"If a girl who is the same age as my daughter dies during a sea passage, each of us can think whatever we like, but let's not let our children think that their parents, for a percentage point in the polls, have given up their humanity," Renzi said.

(Editing by Crispian Balmer and Tom Heneghan)