A POWERFUL group of MPs and peers this week will launch a severe attack on Tony Blair's ambitions to open up Britain's airwaves to American conglomerates - a move which look set to benefit media moguls like Rupert Murdoch.

A joint committee of the House of Commons and House of Lords, chaired by Lord Puttnam, the Labour peer and film producer, will express deep concern on Wednesday at the ''creeping Americanisation'' of British television, which they fear will become much worse if US companies are allowed to snap up parts of the ITN network.

It has been suggested the prime minister is keen to placate Mr Murdoch, the owner of BSkyB and newspapers such as the Sun and the Times, in the hope that his media stable will be less hostile during any euro referendum.

Whitehall sources already have indicated that Mr Blair is prepared to take on the committee over the contentious issue of foreign ownership and is willing to personally sanction overturning its findings - a move described by one government insider as ''extremely rare''.

Mr Blair's position appears to be that it is untenable for the British media to be liable for takeover by European firms and individuals, but not American ones.

However, last night, one member of the committee told The Herald: ''There is concern. The committee did not support the government's position on foreign ownership. It felt very strongly about the lack of reciprocation as well.''

This latter point is a reference to the fact that while parts of British radio and television could be opened up to takeover by US companies, UK firms are barred from taking over American stations.

The joint committee on the draft communications bill claims the government's arguments on the issue of opening up the British media ''lack force'' and are based on ''an untested aspiration''.

It will say if Mr Blair does not do a U-turn on his plans, then British television and radio will be placed in serious jeopardy.

The MPs and peers, who include Lord Hussey, a former chairman of the BBC, argue that American media giants such as Disney and AOL/Time Warner would engage in a ''determined and sophisticated attempt'' to move away from UK-based programmes and concentrate on US products such as The Simpsons and Celebrity Boxing.

The committee will recommend the whole issue should be reviewed by Ofcom, the media's new regulator when it is created, and that the BBC with its ''dominant'' position should also come under the remit of Ofcom on matters of competition with commercial rivals.

It is claimed the committee's recommendations on foreign ownership were finalised after intense lobbying from the BBC and Channel 4.

In May, Tessa Jowell, the media and culture secretary, announced the government wanted to open up ownership of Britain's media.

The move was seen as of particular advantage to Mr Murdoch, who has for some time wanted to acquire a terrestrial-based television station. The proposed changes would allow him to buy Channel 5.

They would further the merger of Carlton and Granada, bringing nearer the prospect of a single ITV company, and relax the rules on radio station ownership. The proposals would also create Ofcom, a single regulatory body for the communications industry to replace the current five watchdogs: the ITC; the Broadcasting Standards Commission; Oftel; the Radiocommunications Agency, and the Radio Authority. Three months of consultation on the draft bill have already started and the legislation is likely to be put before parliament before the end of the year.

Last night, a spokeswoman for the Culture and Media Department suggested that while the government would listen to representations on its draft bill the chances of it changing its mind on the foreign ownership proposals were very remote.

''The provisions on cross- media ownership were not tentative proposals, they were decisions,'' she said.