(Corrects sex of speaker in para 29)
By Gunta Gasuna
TEREHOVA, Latvia (Reuters) - Optimists call it the end of the Iron Curtain. Pessimists fear a "Fortress Europe" or a wave of illegal immigration from December 21, when passports will be checked at fewer European borders.
When the European Union's passport-free Schengen zone expands to include nine mostly former communist states, travelers in the EU will not need a passport to cross land and sea borders in an area about one-third the size of the United States, from Narva in Estonia to Narbonne in France.
From next March the extended zone will also include airports in a total of 24 European countries, where more than 400 million people live.
On what will be one of the front lines between Europe and Russia, chief border guard Andris Bulis is relishing the challenge.
"I feel responsibility, only responsibility -- because all the emphasis will be on the external borders," said Bulis at the Terekhova checkpoint on the border between Latvia and Russia.
He and thousands of eastern European colleagues will become responsible for the EU's borders with neighbors including Russia, Belarus, Ukraine and Croatia: fighting illegal immigration as well as drug- and people-trafficking.
The Schengen zone, named after a village in Luxembourg where a first agreement was signed in 1985 between the Netherlands, Belgium, Luxembourg, Germany and France, has been gradually expanding: but the next extension will be the biggest so far.
After ministers approved it, Czech Interior Minister Ivan Langer said: "The last remnant of the Berlin Wall or the Iron Curtain is falling," according to the Czech news agency CTK.
A key factor in the freer movement of people who live in the area is economic, as red tape is stripped away in the expanded 3.6 million sq km (1.4 million sq miles) zone.
All but one of the new members -- Malta -- are eastern European states, and some anachronistic legacies from "old Europe" will disappear, making life more convenient.
For instance, the town of Valga-Valka on the Estonian-Latvian border will shed border posts in the middle of Seminar street in Latvia, which becomes Sepa street in Estonia.
People traveling between the Slovak-Hungarian town of Komarno-Komarom will no longer have to go through border controls on the Slovak side of the bridge.
So far, businesses seem geared more for an end to petty inconveniences than reform: in the Hungarian town of Gyor near the Austrian border, car maker Audi expects a reduction in losses from delays and hopes planning will be easier.
"Besides employees traveling in a car not having to wait at the border, the real advantage is a more predictable border-crossing process for freight vehicles," said Monika Czechmeister, corporate communications chief at Audi Hungaria.
That freedom has raised fears about an increase in organized crime.
"This has for long been a major fear in the old Schengen states: there indeed have been problems for a long time, they did not have the same level of security," said Jerome Bacquias, from the European Policy Centre, a Brussels-based think-tank.
"But a lot has been done over the last two-and-a-half years, things have truly improved."
He noted there are resources, such as a database of wanted people and missing vehicles, that border guards can use.
In Latvia, Bulis boiled it down to more work for him and his men, and expects illegal immigrants from Russia -- mainly citizens of Ukraine and Moldova rather than Russians -- to be added to his tasks.
While guards on the new fringes of Europe expect more work, there are suggestions that migrants anticipating increased vigilance after December 21 are racing to get to the West.
Jozsef Tanyik, border guard press chief in Nyirbator, near Hungary's borders with Ukraine and Romania, said 70 illegal immigrants were caught in the first few weeks of November, compared with 166 in all of 2006.
"Many migrants who had arrived in Ukraine might have thought it better to get through Hungary before the Schengen entry. That's a mistake, as border control has been just as strong up to now as it will be after," he said.
Border guards in eastern Europe say they can meet the challenge of the extra work, and the EU adds that the end of passport controls inside the bloc will be accompanied by greater cooperation between its members.
In some western EU nations, including German areas bordering Poland and the Czech Republic, doubts have been raised about the effectiveness of border controls run by governments in the former communist states.
In Austria, the government has angered its neighbors with plans for joint border patrols: they say this suggests Austria does not trust eastern European authorities to do a proper job.
In Germany, hundreds of police officers, unusually, staged a protest in November in Frankfurt on Oder on the Polish frontier against plans to remove them.
The police argued the government should leave them in place until a security analysis had shown they were no longer needed.
Miodrag Shrestha, head of Group 484, an organization dealing with refugees and visas in Serbia, said one way migrants might find it easier to travel would be in the fact they would need only one visa instead of several.
"But the European Union and Schengen zone are like a fortress, and the EU is rather picky when choosing who will get the 'exclusive' Schengen visa," he said.
Migrants caught trying to cross into the zone illegally will still face an uncertain future in detention centers.
In one centre in the eastern Slovak town of Humenne, people from India and Pakistan were among those waiting to find out where their future lay, alongside Nijabat Walizada, a 21-year-old from Kabul, Afghanistan.
"There is fighting between Taliban and America and that's why I have escaped," he said. "Because of insecurity, everyday explosions."
Albanian Gjorggi LLeshi from Kosovo, also 21, is awaiting deportation from Nyirbator in east Hungary.
Why did he want to go to the West? "It's a good life," he said.
Writing by Patrick Lannin in Riga, reporting by Zoran Radosavljevic, Ksenija Prodanovic, Sandor Peto, Gergely Szakacs, Martin Dokoupil; Ingrid Melander; editing by Sara Ledwith and Andrew Dobbie