ABOARD LE NADIR -- It was unmistakably a man's outdoor walking shoe, and it appeared as if being exhibited by Abercrombie & Fitch from a painting by Salvador Dali. Beneath the shoe and surrounding it was bright yellow sand. A few feet to the right, a teacup, glistening white, no saucer. And sprinkled here and there, as if to keep a tablecloth from being buffeted by the wind, chunks of black rock formations, about the size of a human wrist. Coal. And all of this I was seeing through a foot-thick glass porthole the size of a kitchen's electric clock.

We were gliding over the target area -- a few acres of ocean floor into which the sinking vessel had disgorged a small part of the paraphernalia of the 2,200 people traveling exuberantly on the maiden voyage of the Titanic across the Atlantic Ocean.

I wondered: Was that shoe I saw covering a human foot on the night of April 15, 1912? The answer can't be known certainly because the men and women who died when the Titanic went down were on the surface of the water, frozen to death. The exception was the engineers who fought bravely below to maintain electric power on the great decks above them.

We stopped to fetch the teacup. By common agreement, the entrepreneurs have decided not to excavate personal articles. But if you pick up (as we did) a pocketbook, open it and find inside a woman's wristwatch, you do not toss the wristwatch out.

The foraging resumed. We (the little, $20 million French submarine Nautile) were looking for three specific objects, previously photographed, one of them a man's valise, the second a part of a leaded window missing from the larger window now reconstructed and the third the loose-lying control levers that had fallen from the bridge from which Capt. Edward Smith had ordered the engines to shut down after the iceberg was hit.

''Turn to 130 degrees, then go for 60 meters,'' the voice from the radio came in, giving the instructions of the navigating coordinator aboard the mother ship, the French Nadir, 2 1/2 miles above us. Georges, the senior pilot, lying on his chest, reoriented the little sub in the indicated direction, and we crept noiselessly forward, one meter above the yellow sand. The copilot, Pierrot, sat on his little chair. He looked through his porthole, the top of an isosceles triangle at the base of which are the other two portholes. And beyond the porthole, Pierrot has two small television screens giving him a remote video view of what lies immediately ahead. To his left are two more little video screens, one of them indicating the full-view action of the prosthetic arm, the manipulation of which permits the Nautile to recover artifacts as dainty as a brooch, done with the precision of a surgeon's scalpel, and either inserted into the submarine's marsupial or, if too bulky, identified with a floating flasher, to be brought up later in a basket made buoyant by huge plastic corks.

My job, as ''observer,'' was constantly to strain my eyes to the right, lest we glide by the objective, and to direct the attention of Georges to any object I thought especially interesting. My problem was that I found everything especially interesting, which would not have been the case after six weeks of diving (it is too fatiguing for the same divers to go on successive days; it is one day on, two off). But soon I came to know when to bid legitimately for the attention of Georges and when simply to think, forget it. Just one more teacup from the Titanic.

It is all being carefully husbanded, scrubbed and put back in saltwater tanks for preservation. A French national laboratory will take it from there. They will have, to exhibit in museums, more than 100 articles taken from the ocean floor, including the doctor's satchel we spotted and the gentleman's gold cuff-link case.

The Nautile is a technological miracle, but if ever they decide at Disney World to imitate it for public consumption, they will need to make generous alterations. On climbing out of the Nautile 9 1/2 hours after entering it, I reached for a description to satisfy the curiosity of a young American associate of the sponsoring firm, who wanted to know what it was like. It is, I said, something like hiring John Kenneth Galbraith, Haystack Calhoun and Jackie Gleason to move into a 1950 Volkswagen and play jointly a Bach toccata on a two-console organ. No one larger than 5 feet 6 inches can -- ever -- stretch out his legs. A cold aluminum bar bisects the stomach if you are lying down peering out of the porthole (there were 6 1/2 nonstop hours of that), and it does the same to your back if you try to lie down (you will) on the 90-minute trip down and the 100-minute trip up. You can sit with your knees bent, but must not lean back. You might push one of those thousand toggle switches -- who knows? -- maybe the one that will add your watch and shoes to the collection on the ocean floor.

It is one hell of an enterprise.