Visions of Libyans, or madmen, or terrorists, or whomever, lurk in our heads, the threats coming and going, but The Threat everpresent.

Action is taken. For example, on the roof of the White House there arises a clatter of a SWAT team said to be armed with sniper rifles. An astronaut touring Capitol Hill gets Secret Service protection. White House aides such as chief of staff James Baker, his deputy, Michael Deaver, and counselor to the president Edwin Meese are now constantly flanked by what appear to be legions of eccentric deaf people -- agents with radio buttons in their ears, and their penchant for mumbling into their hands, where their short-wave microphones are concealed -- "We have movement, we have movement," and so on.

Like any other human beings dealing with fear, we have responded by increasing our observance of rituals: the Secret Service agents running alongside the cars, the sirens, the limousines with the one-way windows, and the metal detector.

The metal detector is Washington's new frame of reference. Literally. It's the kind passengers have to walk through at airports. Now, since the assassination attempt on the president in March, and especially since fears arose of Libyan hit teams skulking into the country (a threat now being discounted in some circles), Washingtonians have had to walk through them at the Ambassadors Ball, at a recent Kennedy Center gala where the president appeared, at the Phillips Gallery and on the White House lawn. They are all over Washington, grandly springing up like arcades of swords at military weddings, or Roman arches on North African deserts.

See the crowd of reporters lining up in front of the White House; see the guests at the Phillips or the Kennedy Center. They funnel down like tornados of humanity to the metal detector that stands between them and proximity to President Reagan.

They almost seem to enjoy walking through it -- putting everyone in the same frame of reference is so democratic. Some of the women are a bit alarmed by the zipper-by-zipper search of their purses, and the men tend to look just a touch foolish in these things, the way they look in barber chairs. But this is the new Washington, huddled beneath its insecurity blanket as visions of death plots dance in its head. Not to mention the terrorism so talked about by Alexander Haig, whose car, let's not forget, was bombed when he was still commander of NATO.

" 'Secret' is a misnomer," says former Secret Serviceman Charles Vance, now head of MVM International Security in Northern Virginia, and husband of presidential daughter Susan Ford, whom he was assigned to guard. "These agents are selected because they are extraverted, the kind of people you notice."

You notice them getting into scrub suits to be in the operating room with President Reagan. Or crawling through ventilation ducts and prying up manholes on parade routes. Or chasing Vice President Bush's speedboat. Or shooting Lyndon Johnson's rattlesnakes. Or watching as a crazed rabbit heads for President Carter's canoe. They've been around for a while, but it's now more than ever.

"You create your own crowd with the motorcade, or with the ropes and the stanchions," Vance says.

The crowds are growing. Observers at the Defense Department note that Secretary Caspar Weinberger's complement of security men has recently grown to include cars that travel in front and in back of his limousine. At the Interior Department, Secretary James Watt has added to his already controversial presence by appearing in public with security men, whose presence is described by a department spokesman as "appropriate." Appropriate for what? (Hit teams of grizzly bears? Snail-darter sapper squads?) "Appropriate for whatever," says the spokesman. Secretary of Agriculture John Block has agents with him when he travels. And was that Secretary of State Alexander Haig, the other day, heading up Rock Creek Parkway in his limo, while the security agents' station wagon, sometimes known as the "war wagon," followed, with agents hanging their heads out the windows like Irish setters?

Nowadays, you never know if it was the president or not. During a recent trip to the Sheraton Washington hotel, the presidential limousine headed up Connecticut Avenue with White House pennants flying, and smoked glass windows shrouding the interior. It pulled up to the hotel empty. The president was riding in one of the following cars, a run-of-the-mill sedan. On another recent trip, the presidential limousine joined the cavalcade of security cars, police cars and war wagon a block away from the White House.

All of this adds to the pageantry of political Washington, and the mysteries of power.

David Kennerly, staff photographer in the Ford White House, and now assigned to the Reagan White House by Time magazine, says: "One of the most impressive things about a presidential arrival is the sound of about 25 car doors opening and slamming. It really gets your blood racing."

A former presidential aide says: "The show is not an inconsiderable part of the protection. A certain number of people are going to be discouraged from attacking the president because the security looks impenetrable."

Henry Kissinger, known for savoring the pomp of all those sirens, the security men running alongside the car, the Uzi submachineguns and so on when he was secretary of state, now pays out of his own pocket to be flanked by ex-Secret Service agents. Kissinger knows the meaning of these things. Once, on the way back from Andrews Air Force Base after a trip overseas when he was in office, his motorcade got stuck in traffic on the Southwest Freeway. There were police cars, there was the station wagon load of agents all staring in different directions, and there was Kissinger's Cadillac limousine, pure heft, as if it were carved out of one solid block of onyx. Inside was little Dr. Kissinger himself, oblivious to the gawkers crawling past in the left lane. So secure and oblivious was he that he perused a newspaper with the aplomb of a man sitting in his own breakfast nook.

Security! Pageantry! No wonder he couldn't give it up! What Washingtonian worth his salt would rather stay home than go through the metal detector? Prestige, here, is being invited to a party where you have to go through one. More prestige is throwing a party where everybody else has to go through one. Ultimate prestige is having metal detectors every place you go but never having to go through them yourself.

Politicians, especially of the appointive variety, are sensitive to these things.

Zbigniew Brzezinski, thenational security adviser who had the misfortune to serve in the ultra-modest Carter administration, was forced to find his security men at the Defense Intelligence Agency. When it turned out they weren't allowed to carry guns, they were deputized as U.S. marshals, and Brzezinski entered the big leagues.

As with all ceremony, it's the thought that counts.

The British post equerries, Beefeaters and men in busbys around their royalty. We need to imagine that all pomp is practical, and so we have security men. They are symbols of what all American men ought to be -- strong, silent, vigilant, selfless and conspicuously inconspicuous. They are samurai of puritanism.

They don't smile.

"Operationally, smiling or laughing is discouraged," explains former agent Vance.

They don't eat.

Think about it: if the Secretary of Whatever shows up at your house and all the security men start dumping hors d'oeuvres into their faces, it gives them the aura of bodyguards, or even worse, henchmen.

They don't have to be introduced.

But they're not servants, either. Get between the person they're protecting and his point of exit, and you can get brisk treatment indeed. Says Kennerly: "It's like being between a pig and a feeding trough."

They're never your guests. You're never their host. One host to a former vice president remembers Secret Servicemen swarming over his property two days in advance, checking out exits, the basement and potential helicopter landing sites. During the dinner, one of the protected guests accidentally hit a button carried in the pocket to summon instant protection, and suddenly the house was booming with big beef packing pistols.

It's protection, but it's also protocol, precision, pomp and pageantry. No detail is too small to escape debate. In 1976, an agent caught an egg thrown at candidate Ronald Reagan on the University of Wisconsin's Oshkosh campus, and was told that he shouldn't have. Four years later, however, egg policy was apparently reversed when a Secret Service spokesman was reported as defending agents for catching eggs tossed at Teddy Kennedy's entourage in Newark, N.J. "They were eggs, but they could have been anything. Our guys didn't know."

Serious business. If hundreds of the world's most powerful people can line up like school children to file through a metal detector, Secret Service agents can catch eggs and not feel foolish about it.

Security is properly regarded by Americans who have it as a nuisance, like all ceremony. Our politicians are all supposed to be Mr. Smith coming to Washington, men of the people, average Joes, Mr. and Mrs. Front Porch USA.

This myth clashes with another one though, with the security agents caught in between. As a press aide for Rep. Phil Crane was quoted as saying, back when he was running for the Republican nomination last year: "The agents have given us a presidential aura."

There's a point at which the returns diminish, however. President Reagan declined to expose himself to assassins this year by going outside for the annual Christmas tree lighting -- the pomp of protection in these fearful times outweighing even the pageantry of Christmas.