The people of the islands of Samoa have become sufficiently Americanized to permit the use of jury trails in criminal cases, a federal judge here ruled yesterday.

The U.S. government had argued on behalf of the territory that its strict caste system and the presence of tribal chieftains who could influence juror's decisions would make the jury system unworkable in the chain of islands 4,000 miles southwest of Hawaii.

However, U.S. District Court Chief Judge William B. Bryant said th "adaptability and flexibility" of the Samoan society and the islands' ability to accomodate and assimilate what he called "the American way of life" indicated to him that jury trails are practicl there. He set aside as unconstitutional the Interior Department regulation that specifically banned jury trails there.

Bryant found himself the arbiter of the Samoan jury trial issue after a U.S. citizen who publishes a newspaper in Samoa was found guilty by a three-judge panel there of failing to pay income taxes. The publisher, Jake King, filed suit in federal court here saying he should have had the option of a jury trial on the islands.

Bryant initially threw out the case for lack of jurisdiction.However, the U.S. Court of Appeals ordered it reinstated and sent it back to Bryant to determine whether the Samoan culture would react favorablu to the jury system.

That is why for several days last summer, Samoan officials in native dress - including males wearing shirt-like, calf-length lavalavas - went before Bryant here to tell him about their islands.

The islands of Samoa have been American territories since 1900 and have been, in the words of Margaret Mead - the anthropologist whose book "Coming of Age in Samoa" is widely regarded as the seminal work on Samao - "externally" Americanized with a constitution and a three-branch form of government.

The islands have been controlled by the military most of the time and have been inundated with modern technology such as a widespread educational television system. Yet they have remained steeped in custom, and Mead testified at the trial that it would be impossible to find a "jury of one's peers" in a hierarchical system such as that which still prevails on the islands.

The president of the Samoan Senate agreed with Mead, saying the islanders would vote on a jury as their matals - or chiefs - told them instead of following their own consciences.

Bryant outlined the "Fa'a Samoa" - or the Samoan way of life - in his opinion released yesterday. It consists of such features as the "aiga," or extended family," the "matal" or chieftain system, the communal owning of farmland, and the custom of "ifoga" in which one family formally apologizes to another for offenses.

Bryant said, however, that the islands' culture is continually changing and has changed to the extent that the jury system would be acceptable there now. He said the manner in which the other portions of the criminal justice system have been handled in the past few years indicated to him that impartial jurors could be chosen among the islanders.

He said he was sympathetic to the view that the decision of whether to begin using jury trials in Samoa should be left up to the islanders themselves. However, he added:

"The fact is that all the hard evidence which bears on the actual situation in American Samoa today in tems of its legal and cultural development . . . leadsme to the inescapable conclusion that trial by jury in American Samoa is not "impartial and anomalous."