Glencore , the world's largest listed diversified commodities trader, has delayed a restart of its 80,000 tonnes a year lead plant in Portovesme, Italy, until 2012 to resolve environmental and technical issues, two sources told Reuters on Monday.

The company has told us that they want to restart the plant by the end of 2012, a senior Italian trade union source said on the condition of anonymity, referring to a recent meeting with the Glencore management.

Sources told Reuters in June Glencore, which put the production line at Portovesme on care and maintenance in 2009, planned to restart the plant after summer holidays.

They still need to verify some issues with the environment ministry and with local environmental authorities, there are some technical questions, the union source said.

There was no immediate comment from Glencore.

The company, which is installing new technology at the plant, has confirmed it was a priority for it to restart the facility, the source said.

My assumption is a possible restart at Porto Vesme no sooner than late 2012, due to Glencore's desire to treat more secondary materials and the necessary reconfiguring of the plant to cope with greater flexibility of feed, said a market analyst.

Along with the uncertain economic outlook for Europe, and slip in LME lead prices since the summer, it may have prompted Glencore to hit the pause button on this one, he added.

A handful of producers have announced plans to curb output of metals in the face of deteriorating economic conditions.

Benchmark lead prices on the London Metal Exchange (LME) were last indicated at $2,024.25 a tonne, down around 30 percent from the year's highs above $2,900 a tonne reached in April.

The analyst also said a new lead smelter was due to come on stream at the company's Ust-Kamenogorsk facility in Kazakhstan in the first half of next year, which will allow refined lead production to rise there.

So maybe there's less need to push lead restart at Portovesme as a result he said.

In October, the International Lead and Zinc Study Group (ILZSG) said it expected the global lead market would be in a surplus of 97,000 tonnes next year following a 188,000 tonnes surfeit this year.

(Reporting by Svetlana Kovalyova in Milan and Karen Norton in London)