Seven months after The Times, Britain's oldest and best-known newspaper, and its sister Sunday Times were rescued by Australian press baron Rupert Murdoch, the newspapers' future again is clouded.

After Murdoch threatened to close the newspapers forever next Monday, printing workers who had interrupted their production in a labor dispute agreed tonight to return to work and promised in writing not to disrupt production again. The 101 printing workers involved gave in to intense pressure from other unions, their own union leaders and British Trade Unions Congress General Secretary Len Murray, who helped negotiate the agreement with Murdoch.

The workers' dispute with the Sunday Times management and another union over pay differentials, manning and jurisdiction is typical of crippling disagreements that have plagued The Times and most of Britain's other national newspapers in recent years, as both management and unions have been squeezed by the industry's growing financial difficulties.

The problems of The Times newspapers appear to go much deeper than this dispute, as critical as it became this week. Murdoch has said he cannot afford to increase the pay of these or any other production workers above contractual amounts. Newspaper industry analysts said losses at The Times and Sunday Times have continued to grow so large under Murdoch's ownership that he will have to cut costs significantly if the newspapers are to survive.

Murdoch also declared today he would tolerate no further interruptions of publication after the current dispute is settled. "If we are unable to produce the Sunday Times and daily Times every day," he warned, "we will close down."

The papers lost more than $8 million in July and August and analysts forecast they will lose $40 million or more this year. Except for when the papers were shut by a year-long labor dispute in 1978 and 1979, this loss would be even larger than those suffered by their previous owner, the international Thomson organization, which subsidized them with profits from North Sea oil investments.

Murdoch said his News International company has put nearly $40 million into The Times, Sunday Times and their various supplements since he bought them from Thompson for more than $25 million in February. Their business and advertising staffs were extensively overhauled, editorial staffs upgraded, and promotion increased.

But The Times has continued losing millions of dollars and failed to increase circulation, while the Sunday Times, with a circulation of 1.7 million and a large printing operation, also has disappointed Murdoch financially.

Despite an agreement negotiated with labor unions when Murdoch bought the papers that eliminated nearly 700 of the newspapers' more than 4,000 jobs, analysts forecast that The Times' losses could consume all of Murdoch's profits from his other holdings here, principally the racy daily tabloid, The Sun, and the equally gossipy Sunday paper, News of the World.

Murdoch's business empire is vast, including newspapers, magazines, television stations, book publishing, film and record production in Australia, Britain and the United States. Despite the rapid financial growth of his Australian holdings in particular, Murdoch does not have anything as profitable as Thomson's oil wells.

Murdoch also has borrowed considerable amounts of money at high interest rates for recent expansion of his holdings, according to analysts and lost large sums of money since buying the New York Post.

This financial picture and Murdoch's past reluctance to dip into his Australian profits to bail out losses elsewhere have led analysts and commentators here to speculate that, even if the current labor dispute is settled, Murdoch could be unwilling to tolerate large losses at The Times for as long as he indicated when he bought the newspapers.

The continuing crisis at The Times newspapers mirrors financial problems all along Fleet Street, where Britain's national newspapers are published. Several others, including the respected Financial Times and Guardian, are reported to be losing money as newsprint and labor costs soar, competition for circulation becomes more intense and advertising suffers from the severe recession.

In addition, the labor unions who control hiring and firing in the printing plants continue to resist most efforts to reduce manning and introduce computerized technology now used in many other countries and some provincial newspapers in Britain.