He wore a blue crew-neck sweater and corduroy pants of kelly green. His shirt was a light blue Brooks Brothers-style button-down and his shoes were tan bucks. He walked quickly, almost jauntily, down Knightsbridge toward Park Lane, seemingly unaware that he is to some a hero, but to others just a rarity -- the American in London. There are no innocents abroad this year.

The streets of London are largely empty of tourists. The restaurants too. The American accent goes unheard in the land, and the collection of what a self-professed pro-American newspaper columnist called "gauche, loud-voiced tourists" and "polyester-suited Midwesterners" cannot be seen searching street maps to find where they are, where they were and where they should be. Untold millions of them have apparently decided they should be home.

The British Airways flight was a traveler's dream -- mostly empty. Almost everyone had a row to himself to stretch out, to sleep. That's nice. On the other hand, the concern for terrorism rides with you too. You check under your seat -- a life raft there -- for the bomb like the one that exploded in a TWA plane over Greece. Then, for good measure, you check your fellow passengers: which one looks like he could have been duped into taking something aboard? Where is the pregnant Irish lady who is carrying more than a baby? What does a suicide bomber look like and -- click, strap yourself in -- what's for dinner?

Let us stick to what we know. I had the duck.

Prime Minister Margaret Thatcher has pleaded with Americans to come to Britain. A member of her party in Parliament, Robert Adley, says Americans are "behaving like cowards" and showing the "natural American characteristic to run away from trouble." Adley, showing the occasional British characteristic to think that courage comes from warm beer and cold toast, makes a hero of me by implication and spoils his case. It takes no courage to travel; it merely takes a ticket, and at Heathrow there is no awards ceremony when you arrive, merely the usual efficient and courteous customs people. If you have nothing to declare, you pass right through.

American timidity in the face of largely imagined terrorism is costing Britain plenty. Last year, some 3 million Americans came here and spent plenty -- an estimated $5.2 billion. This year, the number of tourists may fall by as much as 25 percent. To the chagrin of the British, American logic seems impeccable: in Europe neither the dollar nor your life seems to be worth as much as it was last year.

The result here has been an increase of anti-Americanism and resentment. The case is made that Americans owe a debt to England for permitting British air bases to be used for the bombing of Libya, and the English reward should, at minimum, be the tourist dollar. Instead, the "polyester-suited" tourist is ordering his "cawfee" at Yellowstone. At least there he gets a better press.

The shrinking world has made America nervous. An atomic pot boils over in the Ukraine and some of the spill can be detected in Portland, Ore. Terrorists threaten Americans abroad and also at home. The protective oceans grow increasingly smaller, and America responds by closing in on itself. It will stay home this summer.

In Britain, there is both resentment and envy at America's ability to choose when it will be part of the world and when it will withdraw into its own hemisphere. Americans bomb Libya, and other Americans respond by not going abroad. The British cannot do that; they are already abroad. Their geography limits their choices. America is limited only by its imagination -- sometimes outrageous, sometimes practical but usually fresh. In due course, the ever-shrinking ocean will change that. An exaggerated fear of terrorism may be the first sign that that is happening.

It is May, and the sun plays peekaboo with London. The parks are green and clean, the pubs friendly and raucous, the "cawfee" awful, the cabs still upright like a top hat and driven madly on the wrong side of the road by men who have a nodding understanding of English but cannot speak a word of it. The best advice for the American tourist comes not from the prime minister but from a former president. In a different context, Franklin Roosevelt said the only thing we have to fear is fear itself.

Come on over.