The company employs 7,000 working on radar and defence systems, and electronic projects such as airport security and flight control equipment.
A spokesman for the company, part of the GEC empire, which employs 40,000, said most of the redundancies would probably be compulsory, with the cuts taking effect by the autumn.
The Manufacturing, Science and Finance Union strongly condemned the losses and called for an urgent meeting with the management. "Marconi's madness puts in further jeopardy the future of Britain's vital electronics and avionics wealth-creating industry. It is outrageous that Marconi is considering throwing away the talents of such a huge number of people."
But a company spokesman said growing competition meant GEC-Marconi had to improve efficiency and reduce costs. "There is plenty of business in the export market, but it is fiercely fought for." He said the cuts had nothing to do with recent development problems on GEC contracts for the Ministry of Defence.
Thomson, of France, Italy's Alenia, and Westinghouse in the US are big competitors and have all been slimming down.
GEC already makes the radar for Eurofighter, being built by a consortium that includes British Aerospace. And it is in talks with Thomson and Germany's Daimler-Benz about co-operating on developing a radar system for the generation of aircraft to succeed Eurofighter.
There was better news yesterday for GEC and other UK defence companies with reports that Saudi Arabia is close to awarding Britain a pounds 1bn naval helicopter order.
The Saudi ruler, King Fahd, is anxious to purchase a fleet of anti-submarine helicopters to counter the threat from Iran's new Russian-built Kilo class submarines in the Gulf region.
The British and Saudi governments are understood to be negotiating a deal to sell around 20 EH101 helicopters produced by Westland, part of GEC.
The aircraft will be broadly similar to the 44 EH101s now being manufactured for the Royal Navy under a pounds 1.5bn contract. GEC, Racal and Smith Industries work on the project.Reuse content