LONDON (Reuters) - Sainsbury's (>> J Sainsbury plc), Britain's second largest supermarket chain, is shaking-up its store staff training in a move that puts hundreds of jobs at risk.

The firm said on Tuesday it was doing away with its existing store trainer role, currently held by 870 employees, and would instead introduce around 280 learning and development management positions.

It said existing store trainers could apply for the new, senior roles.

Sainsbury's would look to re-deploy unsuccessful applicants, or those that did not apply, to other roles. Those not re-deployed face redundancy.

A consultation process with all affected staff is underway.

The Unite trade union expressed its "severe disappointment" at the development, noting it came just days after Sainsbury's agreed to pay 1.4 billion pounds ($1.99 billion) for Argos owner Home Retail (>> Home Retail Group Plc).

Sainsbury's, in common with its "big four" rivals -- market leader Tesco (>> Tesco PLC), Asda (>> Wal-Mart Stores, Inc.) and Morrisons (>> WM Morrison Supermarkets PLC) -- is seeking cost savings, partly to finance a price war to try to reverse the loss of shoppers to German discounters Aldi and Lidl.

Sainsbury's is aiming for savings of 500 million pounds ($709.05 million) over three years and has already cut 1,300 jobs over the last year. The company, which trades from over 1,200 supermarkets and convenience stores, has a workforce of 161,000.

Separately on Tuesday monthly industry data confirmed Sainsbury's as the best current performer of Britain's big four grocers.

(Reporting by James Davey. Editing by Jane Merriman)