International high fashion which likes to think of itself as absolutely up-to-the-minute on everything, has come face to face with the theater of the real as it's playing in an Italy besieged by terrorism these days, and which will outstrip the other is anybody's guess.

Already designers, buyers and reporters, gathered to scrutinize 50 fashion shows this week previewing clothes for fall '78, have seen military caps, epaulets, cartridge and hoister belts, campaign ribbons, khaki and camouflage - and that's all on the run-way, not in the streets.

If part of the genius of fashion design is the way it assimilates and expilots trends, it's more predictable than surprising that even Italian terrorism, intensified by the kidnapping of former premiere Aldo Moro and the ongoing trial of terrists in Turlin, has reached designers' drawing boards, Commando berets were a prominent feature at a showing yesterday afternoon.

Buyers siting on the terrace of the Principle Savoie Hotel, downtown, where most of the shows are taking place, cannot see the police van parked beyond the flowering magnolia trees. But before, during and after each showing, police have been checking the rooms and under the chairs for bombs.

The runway has been rightly secured with fabric that is nailed down to enclose the sides so no one can slip a bomb under it.

For the first time that many repeat visitors here could remember, several had their suitcases inspected on arrival and dogs are being used to sniff our drugs and bombs in luggage. Police had planned to checked all buyers' and reporters' bags, according to an organizer of the shows, but were talked out of it.

Not that such measures changed people's minds about coming. About 5,000 buyers and 400 journalists are on hand, according to Mario Goracci, secretary general of the Camera Nazionale Dell' Alta Moda Italiana, and hotel rooms are scarde.

Affluent Italians, meanwhile, are making their own adjustments to the cracking political atmosphere.

"Life continues, but it is different," says Barbara Dessales, owner of a small, exclusive boutique in Milan. "You cannot go out by night, but if you do it is always safer to walk than to take your cars."

Bulgari, jeweler to the super-rich with shops in Rome, Geneva and New York, is making less flashy pieces, but the chairs in his Rome store remain occupied.

Furriers, too, find customers, but their designs rarely show up on the streets of Italy. "You should see the jewels and the furs the Italians all wear when they get to Gstaad," commented one Milanese magazine editor.

Many well to do families have hired bodyguards, but that also has its problems. Bodyguards sticking close to the homes of the wealthy have sometimes been mistaken for kidnappers.

Work goes on, but that's also more difficult. Says Ken Scott, an American-born designer who has lived and worked in Milan for more than 10 years, "The unions are so strong they virtually dictate everything you do. I think they would like to design a collection if they could."

Scott, who has a house in Mexico, is trying to figure out a way to live there part of the year.

In fact, over the last two years there have been fewer strikes, according to Goracci. But a few companies have dissolved into smaller family businesses of under 10 employees so that they don't have to have a union at all.

The Milan shows have been going on only since 1975 when 14 top fashion houses broke off from Florence and established their own group. But Milan is the first of the major fashion centers to display its ready-to-wear (the others are Paris and New York) and so attracts attention.

"Except for Karl Lagerfeld there are more new ideas in Italy than anywhere else," says Roy Witlin of the Nan Duskin stores in Philadelphia.

Adds Norman Silberstein of New York's Alexander's, "The Italians invent it, the French refine it, and the Americans mass-produce it."

One store executive, who asked not to be named, admitted that his customers are rejecting the current "big" look as cumbersome and not good for showing off the figures they have worked so hard to get. "I can't get to a new look fast enough," he said.

Although the big-hitter designers have not shown their clothes yet, there is a new look in store for fall and it seems clear it is intended to include the following:

A tapered look, still roomy but not as big as before

Padded shoulders, making a silhouette that then tapers to them of narrowed skirts or tapered pants.

Slightly more rigid fabrics, with more detail - tucks and quilting.

Lots of leather - lightweight, soft and very expensive.

Oversized "toppers," an extension of the popular blazer for fall.

It was Silvano Malta whose designs for Lux Sport led off Monday's shows with borrowed details from police and military uniforms - velvete battle ribbons and sheriffs' badges tipped with rhinestones. Malta did it with humor, but said, "I have been influenced by the atmosphere and attitude today in Italy. There are more police on the streets."

And as for his camouflage prints, he added, trying to sum up the mood of the city, "For the moment people want to be anonymous. But with style."