BANGKOK, Oct. 7 (Reuters) – The global economic crisis has reduced the role of migrant workers, but that is likely to change dramatically as developed countries face a shortfall in workers over the next four decades, a UN report said.

Demand for migrants will return when economic revival is underway, offering huge administrative and recruitment cost-savings for companies operating in rich countries, the United Nations Development Programme (UNDP) said.

''Following recovery from the global recession, the demand for migrant workers will return,'' said Jeni Krugman, author of UNDP's latest report on migration.

The report called for restrictions to be lifted on the movement of migrant workers, particularly unskilled laborers, to allow them to transfer to other jobs when they become available.

The UNDP also recommended that countries avoid protectionism, liberalize labor laws and stamp out xenophobia and marginalization of migrant workers, whose families benefited greatly from ''social remittances'' sent home.

Earnings by economic migrants from poorer countries were 15 times higher than at home, which meant those employed in developed states were helping to double school enrolment rates and significantly reduce instances of child mortality at home.

The UNDP said demand for migrant workers in developed countries would be higher in the next four decades when domestic workforces shrink. Populations are expected to grow by more than a third in poorer nations. ''Trends in population and demographics are a sign to recognize the need for migrant rights and removal of restrictions on movement,'' the report said.

The findings showed many were working in poor conditions and were viewed negatively because of misconceptions about migrant labor.