The British establishment took a deep breath tonight with the announcement that Rupert Murdoch, owner of the New York Post and racy tabloids in Britain and Australia, is the prospective new owner of one of Britain's most sober national institutions -- The Times of London and its sister publications.

To cement his takeover of the paper, at a cost rumored to be $130 million, Murdoch must clear a number of hurdles.

The proposed takeover has already stirred strong criticism from opposition Labor Party politicians who fear Murdoch's right-wing views and his record as an editor. Frank Allaun, head of the party's media committee, called Murdoch "the worst possible choice" and Labor scheduled an emergency parliamentary debate on the deal Monday.

While the Conservative government has enjoyed support from two large-circulation papers that Murdoch already owns here, many observers think it will have to refer the deal to the Monopolies Commission for consideration.

Under British law the sale may be liable to investigation by the government commission since Murdoch already owns two tabloids, The Sun and The News of the World.

Murdoch must also reach agreement with print and journalist unions, a formidable task given The Times' history of troubled labor relations. He has set a three-week deadline to reach agreements with the unions. The current owner, Lord Thomson, who has said the papers will be closed if a new owner is not found, called for the bids last year.

The Australian press baron, whose best-selling editorial combination of sex, blood and conservative politics has long been deplored by the "respectable" British press, has moved quickly to calm all opposition.

In a press conference tonight he pledged to preserve the "editorial quality and independence" of the paper and noted that his ownership had been unanimously approved by a special Times committee set up to assure that any new owner would guarantee the paper's independence.

"I am not seeking to acquire these papers in order to change them into something entirely different," Murdoch said as he read out two clauses of an agreement pledging him to maintain "editorially independent newspapers of high quality" and to retain the "present board structure" of the papers, including independent directors.

Murdoch got quick editorial support for his pledges. William Rees-Mogg, the impeccably polite editor of The Times, welcomed Murdoch's prospective ownership and said, "I think Mr. Murdoch is the most capable publisher in London and I feel confident he will retain the traditional characteristics of all the papers."

Editor Harold Evans of the Sunday Times, from The Times, said Murdoch's pledges for editorial independence were part of the sales contract and gave the paper's editors the right to "hire, fire and even veto the firing of another editor."

The other properties involved in the sale are a literary and two educational supplements.

"From what I hear, and not having read the small type, the guarantees for editorial independence look better than anything existing in this country," said Eric Jacobs, head of the journalists' union at the Sunday Times.

But other journalists were less sanguine. "Safeguards are very easy to give as pledges, either written or verbal. The problem is to make them work," said Jacob Ecclestone, head of the journalists' union at The Times.

To win conditional agreement from the owners of The Times, Thomson British Holdings, Murdoch had to beat out a number of rival bidders, including Anglo-French entrepreneur Sir James Goldsmith and Lord Rothermere, owner of London's Daily Mail.

Management sources at The Times said Murdoch was chosen because he along appeared professionally and financially able to buy all five titles in The Times group and keep them going.If a deal had not been reached, the paper's owners would have started closing them down in March and face payoffs of up to $96 million to staffs.

But having come to terms with Times management, Murdoch must now come to terms with the print unions. Their opposition to reducing manning levels and to new computerized printing technology resulted in a strike that closed the papers at a cost of several million dollars for 11 months last year. That, combined with the short strike for higher pay by journalists last summer, reportedly led Lord Thomson to sell.

"I am confident that if it is left to the unions and the management we will save the papers," said Owen O'Brien, head of the largest printers' union at the papers.

Murdoch said there will be "considerable" layoffs, and informed sources say negotiations will center on that.