* Hundreds of jobs to go on London's subway system
* Tube boss says losses due to tight financial pressures
* Unions condemn cuts as savage; fear more job losses
LONDON, Oct 7 (Reuters) - London Underground (LU) said on Thursday it would cut 400 back-office jobs and leave a similar number of vacancies unfilled to cut costs on the British capital's subway network.
The company said 400 permanent employees would lose their jobs in areas like administration, legal services and contract management. About 400 roles that are either vacant or staffed by temporary workers will also go.
LU Managing Director Mike Brown said the job losses were needed to save money at a time of tight public finances. Transport unions condemned the cuts as "savage" and vowed to fight them.
A series of strikes on London's underground railway network have caused major disruption in recent weeks. Workers have gone on strike to protest against job losses at ticket offices -- separate from the cuts announced on Thursday.
"Like all organisations, we continue to face financial pressures and have a duty to be as effective and efficient as we can be," Brown said in a statement.
"We have committed to carrying out these changes as soon as possible to reduce uncertainty for those affected."
No train drivers, station staff or mainentance workers will be made redundant in the latest round of cuts, he added. London Underground employs around 20,000 people.
The Rail, Maritime and Transport Union said the Tube network was in "crisis" and it feared more job cuts after the government announces details of public spending cuts on Oct. 20.
"These cuts have nothing to do with ticket offices, they are pure savagery and it shows that all the warnings we have made over the last year were absolutely right," said RMT General Secretary Bob Crow.
Up to 10,000 Tube staff went on strike on Monday in the row over ticket office staff, bringing much of the network to a standstill. The unions plan two further 24-hour walkouts, on Nov. 2 and Nov. 28.
The conciliation service ACAS, which mediates in employment disputes, invited the union and London Underground to hold more talks to try to reach a deal.
"If the parties respond positively to this invitation, ACAS is proposing that talks will take place next Tuesday afternoon," ACAS said in a statement.
About 3.5 million journeys are made each day on the 140-year-old Tube network's 11 lines. (Reporting by Peter Griffiths and Kylie MacLellan; editing by Andrew Roche)