By Shapi Shacinda

KAMPALA (Reuters) - Sierra Leone plans to introduce new laws on diamond trading to boost earnings by ensuring most of its stones are polished before being shipped out, government officials said.

President Ernest Bai Koroma, who won an election in September on a promise to tackle corruption and heal divisions in the war-torn country, said the new policy would be put before parliament "as soon as possible".

"We have not benefited as much as we should have from our mineral resources and that is why we are going to ... put in place a mining policy that will ensure that we move away from having low returns," Koroma told reporters late on Thursday.

He declined to elaborate what the policy would entail or whether it would mean banning or imposing quotas on the export of raw stones.

But a Koroma aide working on government mining policy said: "The idea is to get finished products exported after treating them there ... legislation is inevitable."

This would also create work for thousands of jobless people, said Koroma, who is in Kampala for Friday's Commonwealth Heads of Government Meeting.

"It will not only add value but it will enhance employment opportunities," Bai Koroma said.

Sierra Leone is working hard to rebuild its economy and repair its image after a 1991-2002 civil war for control of its diamond fields, one of the most brutal in African history.

Despite the country's mineral wealth, including diamonds, gold, rutile and bauxite, around three-quarters of Sierra Leoneans live below the poverty line. The government says this is because so many diamonds are smuggled out.

On Wednesday, Sierra Leone banned the export of mineral samples in an effort to stop smuggling, disappointing the diamond industry, which argues the west African nation lacks adequate technology.

At the end of October, Minister of Mines Alhaji Abubakar Jalloh said he would review all mining contracts to clean up corruption and cheating and increase the percentage of revenues that stay in Sierra Leone.

Under a scheme sponsored by the British government's development arm, foreign experts are trying to help the administration overhaul its mining sector.

The UK-led Extractive Industries Transparency Initiative, which aims to ensure government and mining companies publish all transactions between them, is encouraging Sierra Leone to join.