More than a fifth of BBC news journalists are at risk of losing their jobs, the National Union of Journalists said this afternoon, with the flagship One O'Clock News under threat in swingeing cuts scheduled to be unveiled next week.

Jeremy Dear, the general secretary said he believed that "600 to 700 jobs are at risk", out of a total of 3,000, a level that if formally proposed will almost certainly lead to strikes at the corporation in the run-up to Christmas.

Other union sources said they had heard "credible reports" that "the One O'Clock News will go", with the bulletin replaced by a half-hour feed taken from the BBC News 24 channel.

A decision by Mark Thompson to make cuts at BBC News, including the elimination of the separate One O'Clock News programme, is likely to generate political concern.

Although the Government awarded the BBC a lower-than-expected level of licence fee, there was little expectation that heavy cuts in News would be the result.

A spokesman said: "The BBC plans to reprioritise its budget in the light of the Licence Fee settlement have yet to be decided, and will go before the BBC Trust on Wednesday next week.

"Until decisions are made, we have no comment on what may or may not happen."

It is understood that the figures for job losses — out of an expected total of about 2,600 — have not been finalised and will not be until October 17, when the BBC Trust meets to review plans presented by Mark Thompson, the Director-General.

The reductions in News, at slightly more than 20 per cent of the workforce, are far deeper than the 12 per cent expected across the BBC.

A series of mergers between television, radio and online newsrooms are expected in a rationalisation aimed at cutting the number of BBC journalists that attend events.

Union leaders also gave warning this morning of a possible 72-hour strike, amid widespread speculation that 2,600 jobs could go at the BBC, mostly in the next two years.

The unions, led by the National Union of Journalists and the broadcast union Bectu, will deliver their stark message to Sir Michael Lyons, the BBC chairman, in person at 3pm in a crisis summit, arguing that they will ballot for strike action if Mark Thompson, the BBC Director-General, proposes compulsory redundancies.

Gerry Morrissey, the general secretary of Bectu, said: "We understand that 80 per cent of the jobs could go in the next two years.

"I don't see how that can be achieved without compulsory redundancies, and if the BBC gives that to us as a fait accompli we will be looking at balloting our members."

Mr Morrissey added that "any industrial action would be strike action" and held out the possibility of "24, 48, or 72-hour action" that could disrupt programmes at Christmastime.

Previous strike actions have targeted live events, with BBC News staff among the most militant at a corporation already demoralised amid a wave of editorial scandals.

The job cuts are scheduled to be made final on October 17 at a meeting of the BBC Trust, but figures began leaking to union officials today, who gave warning that Mr Thompson was preparing to "salami-slice" the 3,000-strong News operation.

There was little precise detail about how individual programmes would be hit, but all flagship news and current affairs programmes are expected to be affected in some way.

About 18,000 work at the BBC's licence-fee-funded operations, and 23,000 work across the corporation in total.

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