Against a panoramic view of Washington, the soldier in "dress blues" stands rigidly at attention, his M-14 rifle resting on his left shoulder. Carefully and silently, he counts off 21 seconds before walking north 21 steps along the mat in front of the Tomb of the Unknown Soldier at Arlington National Cemetery. There, he halts, turns right, counts 21 seconds, turns right again and shifts his weapon to his right shoulder. He doesn't move a muscle as once again he counts off 21 seconds and paces 21 steps back to his starting point. At all times, he keeps his weapon on his outside shoulder so he can guard the Tomb against any attack.

Outside Fort Myer's Old Post Chapel, the Caisson Platoon waits for the funeral of a colonel to end. When the final words are spoken, the flag-draped coffin is carried slowly by eight soldiers in dress blues who place it on a black caisson and secure the flag. Six perfectly matched black horses, with riders on three, draw the casket-laden caisson, as a sergeant on another black horse rides alongside. Behind the caisson is the penultimate symbol of a fallen soldier -- a riderless black horse, carrying black boots reversed in the stirrups. The band plays a hymn as an infantry officer orders the honor guard to face right and shoulder arms. Slowly, to a muffled drum beat, the procession moves into the cemetery.

Pageantry is the call to arms for the men and women of the 3rd Infantry at Fort Myer in Arlington. They are the elite, ramrod straight, impeccably dressed ceremonial troops of the Army who serve at the parades, funerals, ceremonies and receptions that make up so much of official Washington.

One of the elite is Pfc. Sylvia McDowell, a six-foot soldier, who joined the 3rd Infantry 10 months ago. She used to be afraid of funerals and wakes, but the Army took care of that.

As a member of the prestigious 3rd Infantry, commonly called The Old Guard, McDowell goes to almost 40 funerals a month, sometimes as many as four a day, serving as a casket-bearer or member of the honor guard.

"I've done a lot of things I never thought I would do," says McDowell, a 21-year-old native of Huntsville, Ala.

For McDowell and 1,172 members of the Old Guard, hobnobling with presidents and heads of foreign countries at official ceremonies, is as much a part of their daily routine as their "hut-two-three-four" practice drills that begin at 8 a.m. each day in the woebegotten, dingy gym at Fort Myer.

"I've presented arms to both President Reagan and President Carter and took part in the ceremonies when the Medal of Honor was presented at the Pentagon recently," she recalled, her eyes widening in disbelief. "And I took part in ceremonies on the White House lawn when the president of Nigeria was welcomed a few months ago. When President Carter left from Andrews Air Force Base on Inauguration Day, the television cameras zeroed in on me. My mother saw it and she went hysterical."

Staff Sgt. Robert Faddis, like his comrades, has been to so many funerals, parades, wreath-layings and other ceremonies in his three years as a member of the Old Guard that he's lost count. And like McDowell, he, too, has shown up on nationally televised ceremonies and in Army recruiting films.

"People see us more than any other unit in the Army," says Faddis, a 12-year Army veteran. "A lot of foreign dignitaries see us before they see any other part of the Army so we have to make a good impression of what the Army is."

The 3rd Intantry, established in 1784, is the oldest active infantry unit in the Army, formed before the U. S. Constitution was signed. Its specific mission is to provide security in Washington during civil disturbances and national emergencies.

Assigned to the Military District of Washington, Old Guard troops perform more than 5,000 ceremonies a year, most in this area. Time not devoted to ceremonies is primarily spent practicing for them. In the post gym, in the parking lots near Summerall Field, platoons can be seen at all hours marching back and forth with empty flag standards.

There are seven companies in the Old Guard, including Company A, the Commander-in Chief's Guard, which wears Revolutionary War uniforms and is stationed at Fort McNair.

At Fort Myer are the headquarters company and companies B, C and D, all rifle units whose marching, firing party and casket team platoons share ceremonial and field duties. Company E, the Honor Guard, has the specialty platoons -- guards for the Tomb of the Unknown Soldier, the Army Drill Team, the Army Color Guard and the Continental Color Guard, also in Revolutionary War uniforms.

Company H includes the Fife and Drum Corps, the Salute Gun Battery, the Reconnaissance Platoon and the Caisson Platoon, home of the 3rd Infantry's 31 horses.

Once every five weeks, one of the seven companies is sent to Fort A.P. Hill near Fredericksburg for infantry training. By law, the 16 women attached to the Old Guard cannot participate in infantry training, a source of some complaint from the men.

Col. Don Phillips, commander of the Old Guard, says it is first and foremost an infantry unit; more than 70 percent of the soldiers are infantrymen by occupation and continue to be so when sent to other posts.

But at any give time, Phillips says, 70 percent of the 3rd Infantry, and almost 90 percent in summer when the number of ceremonies increases, is engaged in ceremonial duties.

However, Phillips adds quickly, he has great confidence in the unit's combat readiness.

"This (assignment) is not a soft touch," he says of the long, grueling hours the troops put in. "This is the 3rd Infantry, not the 3rd Ceremonial."

Col. Stephen Perry, deputy commander, adds: "I'd match any of these troops with the 82nd (Airborne). They're smart, they're physically strong and they're handpicked."

Sgt. Faddis, who was in the 82nd Airborne before coming to Fort Myer, has a somewhat different view. "We're definitely trained in Infantry, but I don't think you can be as efficient in it as a unit which trains 100 percent of the time."

Old Guard troops are recruited from all parts of the Army, and the physical, mental and moral standards they must meet are high, says Col. Phillips, because of their conspicuous part in White House, VIP and congressional appearances.

"We are probably the most professional and best-trained infantry batallion in the Army and our tests show it," says Maj. Robert Fazen, executive officer for the 3rd Infantry. "Our skilled qualification test scores are the highest in the Army and it may have to do with the fact that (the troops) are select individuals. And we think our infantry training is better, too."

For the sentinels at the Tomb of the Unknown Soldier, there is an additional hurdle to cross: a 300-question test covering the history of Arlington Cemetery and the Old Guard.

"The Tomb guards are supposed to have the best knowledge of the cemetery because people are always coming up and asking questions (of off-duty guards)," said Sgt. Jerald Wallace, who use to watch the changing of the guards on his off-hours before joining Tomb sentinels.

Nowhere is the spit-and-polish of the Old Guard more rigid than at the Tomb.

It is 2:45 p.m. and Wallace has changed from his jeans to his dress blues in preparation for the 3 p.m. guard shift, one of three he will perform that day. He stands ramrod straight, eyes fixed on the mirror in front of him in the private, wood paneled dressing quarters beneath the Amphitheater in Arlington National Cemetery.

While prospective guards practice with M-14 rifles, guards who will go on duty later in the day are picking specks of lint from Wallace's uniform with masking tape. Alternately, they tug at his "blouse" (jacket) to remove the slightest wrinkle.

Platoon Sgt. Henry Massie, who trained Wallace, scrutinizes Wallace's uniform and rifle before escorting him to the ceremony.

"This is not just a show for the public", says Massie, who knows tourists will be waiting with cameras. "This is a serious business."

"It's a great honor," says Wallace, who plans an Army career. "At night or in the winter time when it gets a lot colder and there aren't as many people around, you get to thinking about everything -- what the job is all about, what you stand for, what your country stands for."

But the Old Guard, with its precision and pride, is not the only tenant at Fort Myer. The Army Band (Pershing's Own) and the Rader Health Clinic, the largest outpatient facility in the Army, are there too.

There are 4,203 people assigned or attached to units headquartered at Fort Meyer, including 3,321 are Army, 542 Navy and 340 Air Force personnel. Among the troops are 752 women.

Col. Walter G. Kersey commands the 256-acre post, established as Fort Whipple in 1861 to protect Washington from Confederate troops and renamed in 1866 in honor of Gen. Albert J. Myer, the founder of the Signal Corps. Among the residents at Fort Myer are the chairman of the joint chiefs of staff and the chiefs of staff for the Army and Air Force.

"I wear two hats," Kersey says. "I'm the post commander, which means I own all the property and have to be responsible for all the tenants, but some of those tenants are totally independent. For example, the Radar Clinic belongs to the Health Services Command, but when they have water or sewer problems and so forth, they're really my problems. But I don't have command over that facility."

In addition to making sure the fort runs smoothly, Kersey also commands Headquarters Company U.S. Army; Headquarters and Headquarters Company U.S. Army Garrison; Headquarters Company Special Activities and the 561st Military Police Company.Army personnel in the greater Washington area are assigned or attached to these companies.

The post that Kersey commands is a meld of old and new, and visitors are struck by the almost college-campus ambience of the fort. Modern buildings and renovated historic structures stand in stark contrast to the dilapidate post gym, originally designed as a riding ring, and the commissary, housed in an old stable; Kersey hopes funds will be allocated to replace the gym and the commissary.

Only the Old Guard is allowed to live in the historic barracks which, like other historic buildings that ring the Rte. 50 side of the post, cannot be touched without approval of the National Capital Parks and Planning Commission.

An old brick fence separates Fort Myer from the Arlington Cemetery and from the county of Arlington, which Kersey says has a good relationship with the post. County and fort fire departments as well as MP and local police forces work together, and the county's human resources department aides troops with such social services as food stamps.

Fostering a cooperative spirit with the post's civilian neighbors is seen by Kersey as a important part of his duties. Kersey himself is on the board of the Arlington Chamber of Commerce and a member of a local Rotary Club, and he encourages other officers to follow his example.

But the heart and the spirit of Fort Myer are reflected every day in the carefully measured paces of the Old Guard, and Kersey believes Fort Myer probably has fewer morale problems than other Army posts because of its unique and sometimes glamorous role.

Sgt. Charles Vassar, curator of the Old Guard museum on the post, agrees: "This certainly beats Camp Swampy"