I HAD THIS crazy idea that I could stay a day longer in the Soviet Union after the congressional delegation I had come with had left for Washington.

I might as well have asked for a copy of the Kremlin's war plans. The impromptu cannot be accommodated in the world's most uptight city.

So I went to the airport on the day appointed, made it through the customs line and even to the proper gate, despite a series of glass baffles that made it tricky.

Everywhere, Russians were watching other Russians; the customs inspector had a supervisor, so did the ticket taker and the passenger agent. It seems to be the Soviet way.

When I arrived in Rome, I went, as always, to the Plaza. It is a splendidly overstated marble pile, with a couchant lion on the last fall of the grand staircase.

I was greeted with the usual cordiality but with the awful news that they had no room. They were expecting me the next day. The desk clerk riffled through the pages of his giant ledger and sighed and groaned and spread his hands: The hotel was pienissima -- booked solid.

But I was in Rome and I knew that somehow it would all work out. I did not need to note how faithful a client I am -- the fact was almost tearfully acknowledged. I just waited.

Finally, after half an hour of flapping and sighing, the ancient porter whispered to the desk clerk, who thought a moment and then said wearily, "Tonight, you will stay in the director's room. Tomorrow, it will be different."

We were not in Moscow.

The next morning, I told the staff about "wetbacks."

"Ah, yes," they said, "Un clandestina," and we all had a good laugh and they joyfully moved me to a splendid room with a terrace overlooking all of golden Rome.

Outside, in the tropical heat, I was taken aback. On the immaculate wide sidewalks of Moscow, people bundled up against the raw cold of late September were trudging along minding their own business. Chic- seeking Soviet women put fringed silk shawls over their stormcoats. It doesn't do much.

In Rome, on the jammed sidewalks, women were wearing T-shirts, covered with sequins, spangles, beads -- some with provocative messages such as "Yes" and "Why Not?" emblazoned on their bosoms.

On the narrow streets, people were chatting, shouting, jostling, ogling, not looking where they were going and conspicuously not minding their own business. I saw a young man almost fall off his bike as he leaned over to inspect a pair of twins whose carriage was being laboriously navigated down the clotted Via del Corso.

On the second night, a friend took me to the Pantheon restaurant. I ate a pasta dish called penne arrabiate -- literally, angry streamers -- which was of a force and savor to clear my palate definitively of Moscow's cabbage. The street scene was of almost unendurable animation, and considerable business was being conducted.

Across from us, a Gypsy child, who didn't look a day over 5, sat down with an accordion in her lap and carefully placed a large plastic offering bucket at her feet. She leaned over her instrument and brought out a few discordant sounds.

"She's warming up," said my companion.

"She can't play," I said.

Indeed that was the case: a few discords, and she would look up at some passerby, who, stricken, would put a coin in her bucket. She checked each contribution before she put her head back on the accordion.

Some of the people streaming by were accosted by a plain young woman dressed in what looked like a motorman's uniform. We got one of her leaflets -- invitations to an apartment for a Scientology personality test.

Presently, another, older Gypsy girl in a skin-tight leopard sheath appeared across the street, gave a minimum-friendly kick to the accordionist and slithered into our restaurant to sell cellophane-wrapped roses.

A block away we spotted the boss, a Gypsy woman, sitting on the curbstone, wrapping roses and keeping a sharp eye on her operatives.

I was a little nervous about the whole thing. I realized I was thinking back to Moscow. The KGB would have swept in and cleared out the whole lot.

I thought back to a conversation I had with a Russian in one of those night clubs for foreigners only. Her only foreign travel had been to Poland and Finland, in which, her shrug indicated, she had not found fun spots.

She said something truly amazing. "We are permitted to go to Italy."

"Italy?" I said. "Are you sure?"

In Rome, I checked. Yes, it was true -- 15,000 Soviet citizens had come there in 1984.

I cannot imagine a more unsettling place for them. They would find out that people unchecked, unsupervised and watched only out of curiosity behave quite well, and that things sort themselves out. They would find out that life can be fun.

I can't think of a more subverive notion for a Soviet.