A tourist grapples with the larger-than-life splendors of Rome

Everyone in the Roman Forum is stumbling over ancient rocks and column bases while holding a guide of some sort in front of their faces. It gives the impression of a dazzlingly sunlit library that has fallen to glorious bits. Some people read aloud to their families. Others narrate to school children. Information is flying around, pouring out of the Blue Guide, the Michelin, and the ''Companion Guide to Rome,'' and the stones just bask in the sun, permitting themselves to be explained.

To someone who is attempting to understand the 2,736 years since Romulus first made peace with the Sabines, the Forum can be a frightening place. Civilization has really gotten the jump on you this time. No wonder everyone is reading as fast as they can, though they have no hope of catching up.

Fortunately, the book in front of this traveler's nose was Georgina Masson's ''Companion Guide to Rome.'' (Prentice-Hall, New Jersey. $8.95.) Ms. Masson writes affably, and she had been chatting me through the old money-lender's hall and around the dungeon Peter was supposed to have been incarcerated in. She had lost me a couple of times when there were repairs being made to an arch here and a temple there. But she got me to the Forum itself and gave me a long talk on just what the Forum was. Too long to take standing, so I sat down, and then, probably for the first time that morning, I looked around.

It was quiet. The white stones were as hot as new bread. The bright blue sky was set off by the baked-out marble bones of the basilicas, temples, and arches around me. The mud-brown, soft tuff stone of other ruins in the background looked like giant African anthills. I felt the sun on my legs and for the first time I felt as if I was actually there. This, I realized happily, was just another piazza. The original piazza, in fact. But a piazza nonetheless.

''A few years ago,'' Masson writes, ''an architectural critic said that Italians today pay little attention to the interior planning of their houses and , like the ancient Romans, have the smallest bedrooms, because they have the largest and finest 'parlours,' in the sense that a parlour is a place to meet and talk in, and that is exactly what a piazza is and what the Forum was, especially under the Empire.'' In short, the ancient Romans were people, too, and you already know something about them if you have had an ice cream in the Piazza Navona or written post cards in front of the Pantheon.

Piazzas not only link you with ancient history, they are good retreats from ancient history, or at least good places to back off and ponder it. You can always drag yourself away from something dumbfounding for an ice cream and a long gaze at whatever it is, which will give you perspective, refreshment, and the will to tour on. The fact that you are doing all this in a public place, along with others in need of the same kind of refreshment, means that it wasn't for nothing that Romulus made peace with the Sabines. Sitting in a piazza, gathering with other thinkers out in the open, you are enjoying the same sense of peace and communication that made establishing a city worthwhile in the first place.

This is a city that feels, in the 20th century, as powerful, busy, fast, grimy, and self-important as New York. Except that there's always a place to sit down, to step away from the surging Fiats and Vespas, and just watch.

If the piazzas are Romans' parlors, they look like they're expecting company. People dress up here, not to be formal but to be beautiful. Chic women, when I visited, liked gray, with short gray pants showing gray-stockinged ankles in gray pumps. Men were well tailored, whatever their shape, and sleek-haired. And even the lady who fed the pigeons in my favorite square did so in a well-cut suit with a snappy shopping bag from St. Tropez full of bread crumbs.

There's something flattering about piazzas. Women pushing strollers hung with shopping bags seem to be doing so in a play, and the fountain is usually in such a focal spot that it gives importance, almost gravity, to flirting teen-agers leaning up against it. All over Rome, amidst the deepest, darkest piles of sooty stone and around the most formidably rococo corners, these little spots in the sun open up and invite you to be seated. Besides, there is a group of fascinating people at the tables who seem to have been waiting for you to join them.

The Forum is a good place to start seeing Rome. You might as well start at the beginning, though you will never get to the end. There are few signs, and it's not always easy to figure out what everything actually was, so you need help, but not necessarily a human guide. ''The Companion Guide to Rome'' did well by me. It is clumsy to hold a thick book and read long sentences as you walk, which is as it should be: You need to sit down. Wear light clothes and good sturdy shoes, since the Forum always seems to be a little hotter than the rest of Rome.You finish up just after noon. Georgina Masson guides you out the gate by the Colosseum, gives you a little nudge, and suggests some places for lunch. I didn't budge, but ate what they were selling by the gate - Italian ice and potato chips. Bring something with you instead and eat it on the Palatine Hill, a high, breezy place, the ruins of an ancient upper-class suburb, in whose villas fabled dinner parties took place, with songbirds for entertainment and larks' tongues for appetizers.

The palaces are spread out. The information is thinner up here, too; the hill is more a park than a library. If you stay till dusk, sunset over the forum is gorgeous. It's even prettier if you look down from the Capitoline Hill, at the other side of the Forum.

''You might as well get started on the Vatican Museum,'' a helpful friend suggested, adding that actually seeing everything in this treasure trove (the Blue Guide calls it ''stupefying'') would take at least a lifetime. This perspective in mind, I bought a Vatican Guide, with different-length itineraries mapped out, which would have been more helpful if I understood it, but basically I did a three-hour jog, taking in the incredible Raphael rooms, literally plastered with Raphael paintings. These are all gorgeous, but the showiest is the ''Deliverance of St. Peter,'' in which the angel who frees him from his chains blasts light through black prison bars. Out of breath, I emerged at the end of every Vatican Museum outing: the Sistine Chapel.

You know you've arrived, because it's so crowded and silent. Overhead is a far more glorious crowd, but just as dense. Michelangelo's figures, at first sight, seem to be involved in a very solemn dance, they are ranged so rhythmically around the ceiling, and their muscles are so beautiful. But you don't see it as a whole after the first glance; the different scenes command and divide your attention. After you have looked enough, the people below look strangely noble. You have had your eye trained, for a moment, by Michelangelo's , and you can imagine for an instant what he would make of all these rolling eyes, thrown back heads, upraised arms, figures clustered confidingly around a Michelin guide, and loners leaning back in awe.

The Vatican Museum, unlike many in Rome, is open in the afternoons from April to October. Most other museums close at 2 p.m. I wouldn't recommend seeing another museum in the morning, though. Afterward, you'll want to let Michelangelo's vision settle. This is a perfect time to do some serious piazza loitering.

Trastevere, on the same side of the river as the Vatican, is an old, close neighborhood. The church of Santa Maria in Trastevere, which has mosaic palm trees on its face, has lost half the numerals on its clock. They seem to have faded or dropped off. What better encouragement to while away an afternoon in the darkened gold, cobbled piazza in front of it? Sabatini is a terrific restaurant with a fire burning and lovely displays of the day's fresh food laid out as you go in, as well as tables outside. Their seafood is exquisite. There is a cafe next door for snacking and gazing.

The Piazza Navonna is a good place for ice cream and Bernini. Tre Scalini serves tartuffo, a deep brown blob of intensely chocolate Italian ice cream with whipped cream on top. Bernini's fountain, The Four Rivers, muscles and sprays flamboyantly; people sit on benches, children play, and artists sketch. The houses around this long, round-ended square are high and elegant.

The Piazza della Rotonda, in front of the Pantheon, is my favorite. Because of repairs, the Pantheon's interior space is limited, and a sign by the door says, ''Do not explain interior.'' So tour groups are briefed in the piazza before they go in. No problem. You can only hear the explanations by trying, and there's plenty of room for piazza-loungers like me. Several small streets feed through, so as you sit, motorcycles, bicycles, and pedestrians sift past.

The Pantheon looks like a huge ball that touched down in the middle of an otherwise ordinary old neighborhood. Its spherical dome is as high as it is big around, and these proportions delight you, whether you're inside or out. Inside , it's lit by a circular hole in the roof. It was finished in AD 125 or 128, but I can't imagine it ever being more of a wonder than it is now.

The Borghese Gallery, with its stippled false-marble walls, complicated floors, and larger-than-life Bernini statues, is a treasure. David winds up to hurl a stone at Goliath, his forehead muscular with determination. It's also Bernini's self-portrait, which helps explain where the wild vigor of these baroque statues comes from. Apollo grabs Daphne. As his hands sink into her white waist, carrotlike roots spring from her toes and bark grows on her shins. She is turning into a tree.

A walk in the gardens of this 17th-century villa is a good ending to a trip to Rome because, even more than the half-clock in Trastevere, it gives you a feeling of timelessness. The umbrella pines have trunks as graceful as Daphne's legs. At noon, people walk their dogs as slowly and thoughtfully as if they were in a museum, stretching the Roman lunch hour to infinity. Practical Information:

Hotel Sole al Pantheon, 63 Piazza della Rotonda, is a nice, small hotel in a quiet neighborhood. When I was there, there was a family atmosphere with young German girls calling home on the phone in the lobby, then relaying messages to the concierge from their parents, who had evidently selected him as a guardian. A good choice. He had plenty of information - and concern for his guests. A single room with bath was around $20, and you could hear the German girls thundering up the stairs, but no traffic sounds.

Giolotti, on Via Degli Uffici del Vicario, has wonderful ices. Melon, hazelnut, raspberry, and chocolate are only a few flavors. Just off the Piazza della Rotonda.

Camillo, on Via di Campo Marzio, is a pizza place. It has zucchini, mushroom, anchovy, potato-and-rosemary, and mozzarella pizza, as well as the standard tomato sauce, and they charge (very little) by weight. Via di Campo Marzio, a narrow street which runs from Piazza san Lorenzo, is a wonderful one to trot down in the evening, say around 6:30, with Italian shoppers buying perfume, vegetables, or other gorgeous daily neccessities.