Cool and calm is fine for astronauts -- but for a presidential hopeful?

The quiet, modest hero walked around the breakfast table, smiling as he shook hands with some 30 reporters but never showing much emotion.

This was the man who was the idol of the nation 20 years ago as he became the first human to orbit in space. However, now the question was being asked in varying ways, but persistently: Is the cool, unflappable personality that made John Glenn a great astronaut what the country now is looking for in a president?

Yes, said the senator, he was aware of the view that he was too reserved to gain voters' attention in a race for the Democratic presidential nomination. ''Once this perception of you gets started,'' he said, ''it is hard to change it.

''But,'' he said, ''I do have passion for my country. I felt that passion on top of that booster (at Cape Canaveral).''

''Then,'' asked a questioner, ''you see no need to shout?''

''I see no need to hoot and holler,'' he said. ''I think back to my pilot days: The pilot who sounds the best may not be my choice for a pilot.

''The content and style of my speeches have been well received. . . . I do feel strongly about the need for a change in this country.'' He said he believed that his message, despite his low-key approach, was being heard by the general public.

Further addressing the question of voter appeal, Glenn referred to his ''big win in Ohio'' in the 1980 Senate race. ''I won by a record 1.6 million,'' he said. ''And Ohio is a bellwether of the country -- its business interests, its ethnic groups.''

The senator pointed out that he had not yet fully decided on seeking the presidency. And here a questioner asked: ''But aren't you digging a hole by waiting? Won't Kennedy and Mondale get out so far in front that you can't possibly catch them?''

''No,'' said Glenn. ''I'm not sitting back. There have been several articles about my possible candidacy that have been favorable. I will be forming a political action committee soon. An announcement of candidacy by the end of this year would not be too late. There would still be 13 to 16 months before the first state caucus and primary.''

''But,'' a reporter asked, ''won't your candidacy simply split the vote for Mondale and assure the victory for Kennedy?'' ''No,'' said Glenn. ''I don't see it that way.''

As a good friend of the Kennedys, particularly Bobby Kennedy, do you have any trouble running against Teddy Kennedy?

No. This is not a footrace. I look forward to doing what I think is best for the country. My running will not be on a personal basis.

How would you separate yourself from the Kennedy ideology?

Let Kennedy, and Mondale, speak for themselves. I have never tried to place myself ideologically, as a conservative or a liberal. I believe in taking each issue as it comes and doing what is best for the country. But however you define the political spectrum - in terms of government spending, etc. - I think I am in the middle of that spectrum.

What has caused the big federal deficit?

The past 40 to 50 years of programs gave us some of it. Some programs have gotten away from us and become a burden. And we have lagged in not correcting these programs.

How do you stand on the so-called social issues?

On abortion I am pro-choice, not pro-abortion. This has been my constant line. I don't think anyone can dictate when life starts.

On tuition tax credits, I am opposed. I don't think the government should support private schools.

On school prayer, I am against mandating it. No one child should ever feel he is an ''outsider.'' I approve of a silent prayer. No one standard of prayer should be set up. . . .

How do these positions affect your presidential prospects?

These lobbies were all against me in Ohio and I came out well.

The AFL-CIO is going to endorse a presidential candidate before the caucus in Iowa. What do you think about this, since labor is not as crazy about you as it is about Kennedy and Mondale?

I met with AFL-CIO leaders recently and was well received. At first I had labor opposition in Ohio. Since then it has given me good backing.

What would you do about unemployment?

I would keep the retraining program. And I'm thinking about the possibility of having an educational fund for workers to borrow from -- a borrowing fund for retraining and reeducation -- but where, at some point, through the use of the IRS, the loan would have to be paid back.

What is your position on limiting nuclear arms?

I opposed SALT II before. But I would vote for it today because we can verify now. Overall, on nuclear arms I would limit expansion, seek reduction, prevent the spread of nuclear arms around the world to other nations, and involve other weapon states in the negotiating process.

Are there any inhibitions as a presidential candidate in criticizing Israeli policies?

No, you have to vote your conscience. And I have drawn the criticisms of Jews at times -- on my vote on the F-16, for example. . . . And many Jews today are critical of Israeli actions in Lebanon.