It was his day off, and he decided to spend part of it on his hobby, photography. He wanted to make some pictures of the Washington Monument.

However, soon after he set up his tripod on the grass near the Monument, a Park policeman showed up. "Do you have a permit?" he asked.

"A permit?" the photographer echoed. "To take a picture in a public park?"

"It's not the picture, it's the tripod," the policeman said. "You need a permit to use a tripod."

The photographer had no permit, so he folded up his tripod and departed. The next day he asked me why one needs a permit to use a tripod in a public park.

I was as much in the dark as he was, so I took his question to the National Capital Region of the National Park Service, where I was passed along to Fran Giarth, administrative assistant to he director of public affairs. Mrs. Giarth confirmed at once that the policeman was right.A permit is required when a tripod is used on Park Service land or inside a public shrine under Park Service jurisdiction.

Why? Because tripods can "dig up turf and scratch marble floors," and because commercial photographers and film crews sometimes try to misuse nationl shrines. To keep some measure of control over the great numbers of professional photographers who are forever shooting pictures at points of interest, the Park Service wants each of them to get a permit before filming begins. And as a result, it processes about 1,000 permit requests per year.

How much red tape is involved in getting the permit? Very little. "Just give us a ring - 426-6700 - or drop by and we can issue the permit on the spot," Mrs. Giarth said. Only on rare occasions is a permit refused to an applicant. "We try to make them aware that they must take care not to damage anything or interfere with the average visitor's enjoyment of the park of shrine. Usually we can work things out so that the public interest is protected."

When Mrs. Giarth finished her explanation, I said, "I can see the need for permits, I guess, but it still seems a little weird that if I hold the camera in my hand it's legal, but if I rest it on a tripod it's illegal."

"Are you talking about First Amendment rights?" she asked.

That spun me around for a moment until I figured out what she was getting at. "Is there a difference between my rights as a citizen and my rights as a newspaperman?" I asked after I had gotten my bearings.

"Oh, yes," she said. "We don't bother the news media. Under the Constitution, you're free to set up a tripod."

"But if the man with the tripod has no press credentials, he's in violation?"

"Well, yes," was the response. "In 99 cases out of 100, the use of a tripod indicates the presence of a professional or commercial photographer.We need some kind of criterion to identify the professional, whose presence we must monitor - and the tripod is the best criterion available to us."

As soon as we finished our conversation, I looked up the First Amendment, and a lot of steam immediately went out of my argument. Apparently there is a sound basis for exempting the press from restrictions that apply to others. The First Amendment says:

"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the government for redress of grievances."

Everybody's freedom of speech is guaranteed, but there's no guarantee that everybody has the right to set up a tripod on Park Service land. Only the press is covered.

At that point, I found myself wondering whether the Fourth Amendment might be more pertinent. That one says, "The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searchers and seizures, shall not be violated . . ." Used in the plural, as the word is here, "effects" are "movable property, goods." So the Fourth Amendment does forbid the unreasonable seizure of tripods.

Now all we have to do is get a court decision on whether the Park Service tripod regulatioon is reasonable. I suspect it is.

Until the issue is resolved, remember: If your objective is to be mistaken for a pro, use a tripod. If all you want is the picture, steady the camera against a tree, take a deep breath, and shoot.