LONDON, May 23 (Reuters) - The Belgian government plans to publish a royal decree that tightens the quality of motor fuel exports within days, with the new regulations expected to take effect after three months, the energy ministry said.

The decree, which aims to tighten the minimum specifications of fuel exports principally to West Africa, mirrors a similar move in the Netherlands last year to bring a halt to the historically lucrative trade of looser-specification gasoline and diesel out of Amsterdam-Rotterdam-Antwerp (ARA).

Already signed, the decree will be published within days, with its obligations taking effect three months later, a spokesperson for Belgium's environment minister Zakia Khattabi told Reuters.

The decree was Khattabi's initiative, carried out in collaboration with the energy and public health ministries.

"This ban targets oil companies that, primarily from the port of Antwerp, export motor fuels with excessively high sulphur or benzene content worldwide," the environment ministry said in a statement.

"These are fuels that have long been banned in Europe due to their harmful effects on public health and the environment."

The loss of Northwest Europe's major blending and storage hub for exports of refined fuels to West Africa creates a logistical headache for refiners and traders over what to do with the structural oversupply of low-quality, cheaper fuel that would not be permitted in local markets. (Reporting by Ahmad Ghaddar and Robert Harvey; Editing by Clarence Fernandez)