(The following is the second of a three-part feature. Part I appeared yesterday; Part III will appear tomorrow.)

REAL OR imagined threats to national security have been used more than once as a handy umbrella for investigations actually aimed at those whose political activities and beliefs the government doesn't like. During the fifties, the supposed dangers of Communism served as an excuse for Congressional investigating committees to delve into the personal affairs of large numbers of Left-leaning American citizens. Now the alleged activities of Weathermen are being cited by the Justice Department as grounds to conduct Grand Jury investigations of radicals.

Five politically active individuals from Venice, California were jailed last year when they refused to answer broad questions that Guy Goodwin, a special assistant in the Justice Department's Internal Security Division, asked them at a Grand Jury investigation in Tucson, Arizona. Typical questions were:

Describe every trip you took outside metropolitan Los Angeles during the year 1970. Where did you go? With whom did you go? What did you-do when you arrived at your destination?

Describe every conversation you had at the apartment at which you lived last year, name everyone who was present and tell what was discussed.

Describe every demonstration, riot, and civil disorder in which you took part last year.

Describe every contact you had with [a certain person] last year.

Officially, the Grand Jury in Tucson is investigating possible violations-by three "SDS-Weathermen"-of the antiriot act and of federal law pertaining to the purchase and interstate transport of explosives. It has already indicted one of the three, John Fuerst, for illegally purchasing 120 sticks of dynamite in Tucson last May and transporting them to California.

But the questions the five Venice witnesses were asked indicate that the Justice Department was not interested in obtaining evidence about a specific crime from them. In their case, at least, the Department seemed to be engaged in a "fishing expedition," aimed at obtaining whatever evidence the witnesses happened to supply.

Some of the five jailed witnesses were asked if they had made any trips outside California during the year 1970 to plan a riot or demonstration and, if so, who had accompanied them. And most were also asked to describe every contact they had with explosives or firearms during the preceding year, every conversation they had about explosives or firearms, who else was present, and where the conversations or contacts took place.

But the witnesses were not asked any specific questions about a plot to bring explosives to California. One was asked a number of questions about a TDA demonstration at U. C. L. A. last February-several months before the alleged Weatherman plot was executed.

Witnesses at a Grand Jury investigation have a recognized right to remain silent if they believe that their answers might incriminate them. But the Attorney-General can request that witnesses be granted immunity from prosecution for their answers and be made to testify, if he personally decides that the national interest requires their testimony. On the grounds that the Tucson Grand Jury was investigating crimes which threatened the national security and defense, Attorney General John Mitchell requested that the five Venice witnesses be granted immunity and ordered to testify. Their answers could of course be used against others.

The witnesses continued in their refusal to answer questions on the grounds that the questions they were being asked were vague and irrelevant and violated their rights under the First, Fourth, Fifth, Sixth, and Ninth Amendments. They placed particular emphasis on the First Amendment, which protects free speech and association. But the district court judges hearing their cases sentenced all of them to jail for contempt.

The first witness, Teri Volpin, initially received a two-month sentence. When she was released in January, she was immediately subpoenaed again, though the Justice Department clearly knew that she would refuse to testify again. When she insisted on remaining silent, she was returned to prison-this time for the remainder of the Grand Jury investigation. The Grand Jury will probably adjourn on December 31, 1971.

Three of the other witnesses-Karen Duncan, David Scheffler, and Pamela Donaldson-were sentenced to remain in jail until the end of the investigation after their first refusal to testify. One witness, Lee Weinberg, will be released on March 31. She will probably be subpoenaed a second time, like Volpin.