* Agadez was a boomtown before security action

* Some experts hope for breakthrough in migrant crisis

* Others say trafficking has gone deeper underground

By Omar Saley

AGADEZ, Niger, Jan 31 (Reuters) - In a dirt-floored room in the town of Agadez in Niger, a pair of flip-flops and a cold pile of ashes are all that remain of what was once a teeming stopover for migrants preparing the fraught journey across the Saharan Desert and onwards to Europe.

Less than a year ago, Agadez was a boomtown - a hub for smuggling networks that profited off migrants seeking a better life and opportunities in Europe. But that was before the European Union, working with Niger's government, bankrolled a crackdown on the trade.

"We have seen the numbers fall dramatically since August," said Marina Schramm, deputy chief of mission at the International Organization for Migration, which monitors migrant flows at two points in the Agadez region.

"Before, we saw several thousand passages per week. Now we're close to zero ... several dozen," she said, noting that numbers normally fall in the winter, but not by so much.

Some are holding up Agadez as a sign of a breakthrough in tackling the migration crisis. Other experts have urged caution, saying the smugglers may have simply moved deeper underground.

Either way, the immediate impact on the town and the arid region surrounding it is dramatic.

The European Union said that only 1,500 migrants crossed Niger in November, down from 70,000 in May, crediting the change to a new partnership strategy it launched with Niger last year.

In late 2015, the EU established a fund with 1.88 billion euros ($2.01 billion) aimed at addressing migration originating across West Africa's arid Sahel and Lake Chad regions, the Horn of Africa as well as North Africa.

Last year it added another 500 million euros to the fund and established partnerships with priority countries Niger, Ethiopia, Senegal, Mali, and Nigeria, financing a range of programmes from security and border management to job creation.

The EU began training security forces in Agadez in April. By November authorities had seized 95 vehicles and arrested 102 smugglers as well as nine police officers for migration-linked corruption, it said.

DRIVEN UNDERGROUND?

Despite those initial results, the EU acknowledged in December that the reduced traffic in Niger had not yet led to an overall reduction in arrivals in Europe. More than 181,000 migrants took the North Africa to Italy route in 2016, more than in any other year on record, though many likely arrived in Libya before the crackdown in Niger began.

Smuggling could have just become more clandestine, said Peter Tinti, a senior research fellow with the Global Initiative against Transnational Organized Crime.

Tightening security often allows smugglers to charge a premium and can push migrants to take riskier routes, he said.

"If it's not done right, anti-smuggling policies can increase smugglers' profit margins and decrease migrants' security," he told Reuters.

Meanwhile, economic development programmes funded by the EU to alleviate the poverty that pushes migrants to leave home in the first place could take years to show results.

In Agadez, the immediate impact of the EU plan has been an economic bust. Streets that used to be thronged with money changers, phone sellers and car mechanics are now quiet. Smugglers' compounds that housed hundreds of migrants are empty.

"I used to live here with lots of friends," said Guinean migrant Boubacar Lu, walking around one of the compounds with "remember me" and other messages scratched onto its clay walls.

"Measures were taken, things changed." ($1 = 0.9355 euros) (Additional reporting and writing by Nellie Peyton in Dakar; Editing by Joe Bavier and Andrew Heavens)