The building is said to meet the highest environmental standards

The new building is said to be part of a drive to spread the economic benefits of working for the assembly across Wales.

The three-storey building at Rhydycar is the first of three regional offices to be opened under the scheme.

Mr Morgan said the new building for 450 staff would provide a "significant boost" in public sector jobs.

"This assembly office will help to shape a more vibrant Merthyr and Heads of the Valleys," said Mr Morgan.

"It offers high quality jobs, economic benefits and much broader career paths for staff."

He added that it would be a "magnet" for inward investment and would improve the attractiveness of the area.

Staff have been working in the building, which is said to meet the highest environmental standards, for the last three weeks.

First Minister Rhodri Morgan unveiled the plaque

The civil servants who work there deal with issues including social justice, housing and European funding.

The aim of the move is to make the workings of government and civil service jobs more available to people outside Cardiff.

So far around 60 people have been recruited locally. The rest moved with their jobs from the capital.

Building work on others assembly regional offices in Llandudno Junction and Aberystwyth is expected to start soon.

The assembly government hopes to have 60% of its staff working outside of Cardiff by 2008.