In a notable victory for press freedom. The Sunday Times won permission today to serialize a searching study of one-time whiz kid Jim Slater.

The decision by the three-judge Appeal Court ends a long battle by Slater and his former partner, prominent Conservative politician Peter Walker, to prevent a critical account of their multimillion-dollar operations from reaching a mass audience.

Even more important than this outcome, according to editors here, is the condemnation by Lord Denning of the use of an injuction to muzzle the press. Denning, Master of the Roll or chief Appeal Court judge, said:

"The press should be free to publish fair comment on matters of public importance and no court should grant an injunction to restrain a newspaper from doing so, exception the most extreme circumstances."

It is common practice here for politicians, businessmen and other prominent persons who do not want press exposure to seek an injunction or court order prohibiting publication. British judges tend to be far more sympathetic to these pleas and pay much less attention to press freedom than their counterparts in the United States. So the device, along with libel suits and contemptactions, frequently muzzles the British press.

If Denning's rule is followed, the injunction technique has been dealt a crippling blow for "matters of public importance."

The Sunday Times intends to begin serializing the Slater Walker study on Sunday with the first of five extracts. In all, it will publish about 30,000 words or nearly one-third of the book produced by its staff member, Charles Raw.

Raw's research into company and stock market records led him to charge Slater Walker with manipulating stock prices in companies with which Slater was connected.

The Slater Walker company fell apart two years ago, but the Bank of England bailed out its creditors and investors with more than $200 million in loans and guarantees.

The government has not held a public inquiry i to the case, and Raw's efforts to publish have been held up by a complex series of legal maneuvers, including a court ruling in which Slater and Walker were able to prohibit any publication until they were satisfied with what Raw hads written.

Last summer Slater disclosed that he was writing his own version of the story.

On the strength of that, Raw was given permission to publish his book yesterday, the same day that Slater published his book. But the judge insisted that The Observer as the only newspaper permitted to carry the material.

It was this portion of the order that Denning and his fellow judges threw out today.