THE HISTORY of Fredericksburg, Va., is the history of America in a nutshell. The city's visible history extends from about 50 years before the Revolutionary War to some of the more unfortunate aspects of modern times.

The town was founded in 1727 at the northernmost navigable point on the Rappahanock River, where ocean-going vessels docked with cargoes for all of northern and eastern Virginia. Capt. John Smith of Jamestown, 100 miles away, explored the area in 1603, and it became a settlement before the end of that century.

The huge, bustling city of the mid-1700s could have become a huge, bustling city of the 1900s, but first the railroads and then the highspeed highways drained off its importance in commerce. Now Fredericksburg is a sleepy but proud city of about 15,000.

The names of persons who have lived or visited there reads like the index of a comprehensive American history book.

We began our tour of Fredericksburg at the visitor center on the edge of the downtown area. There we bought a guidebook for $125. received a pass for free parking (which we never had to use), and for $6 each bought block tickets that admitted us to seven historic sites. The block tickets save about a third over seven separate admissions.

The first stop was the museum, located diagonally across the street from the visitor center, where we got acquainted with the history of Fredericksburg, partially through a slide show dominated by poor-quality slides. We deviated from the main walking tour to stroll tree-shaded residential streets southeast of the historic area, where homes range in style from sidewalk-hugging wood colonial houses to huge brick Victorian homes, some with adjacent servants' quarters.

Returning to the main tour, we passed the train depot and the home of John Paul Jones and walked northeast along Caroline Street, the main business street, which is dominated by antebellum buildings. Workmen were tearing up the street readying it for a traffic-free pedestrian mall.

The Hugh Mercer Apothecary Shop, second stop on the tour, is fascinating, with its contents of pharmaceutical and medical items from the pre-Revolutionary War years. A very pleasant woman in period costume explains it all. She also points out, in the Mercer living quarters above the shop, something we had never seen in our frequent tours of historic homes -- a tiny wig room. Mercer would stick his head through a hole in an upstairs door while a servant in a closet-like enclosure on the other side powdered Mercer's wig. This way Mercer would not get powder on his clothes.

Less than a mile up the street from the visitor center is the Rising Sun Tavern, the center of life for years after it was built by George Washington's brother, Charles, about 1760. It soon became a meeting place of early patriots who laid some of the groundwork for the American Revolution.

Guides paint a fascinating word-picture of tavern life in those days, including mention of all the famous persons who trod the floor the tourists are standing on.After the guided tour, a pleasant drink concocted of tea and fruit juices is served on the back porch.

Next on the tour were the old law offices of President James Monroe who, like George Washington, Robert E. Lee and James Madison, was born nearby. Monroe practiced law in the building from 1786 until he became President in 1816. The museum and library there now contain many of his presidential possessions, including the desk at which he penned the Monroe Doctrine.

George Washington built a house for his mother, Mary, in 1772.She died in the house in 1789, shortly after her son left for New York to become our first President. The house is next on the tour.

After that is Stoner's Store, a block away and chock full of items that could make an antique lover go mad with desire. The building houses 13,000 articles from the past two centuries, the fruit of 50 years of collecting by D. Letcher Stoner. The material is arranged to resemble a general store of the past century.

The last stop on the block ticket is the most beautiful of the Fredericksburg sites, the Kenmore mansion, dating from the 1750s. It was the home of Washington's sister, Betty, wife of Col. Fielding Lewis, who went broke making arms for the revolution. But Lewis left behind a mansion set away from the street by a brick wall and lush, landscaped lawns and gardens. Until he died in 1782 and his widow had to sell the home to pay debts. Betty and George's mother, Mary, traversed the two blocks between their homes on a brick path Mary had constructed. Gen. Lafayette used the path when he came calling after the war.

At the end of the block tour, tea and gingerbread are served in the Kenmore kitchen, a separate building next door to the mansion.

Although we visited on a Saturday at the end of June, we encountered few tourists on any of the stops. That could be because Fredericksburg is poorly promoted despite its beautiful historic district. As an example, how many people know this is the city's 250th anniversary year?

One of the victims of this and other changing tourist habits was the Princess Anne Inn, which closed last November after being unable to keep up with city codes while battling a dwindling clientele. An inn had been on the site since the late 18th century.

The present building is a beautiful, two-story, red-brick affair with large white columns on a rounded porch. Plaques beside the doors boast of visits by Robert E. Lee, Daniel Webster, Lloyd George and Winston Churchill.

The motorist is forced instead into one of the clean but predictable formica-and-concrete motels strung along I-95 west of town. Rooms average about $20 double.

We returned to town in the evening to dine at the Happy Clam Restaurant on the western edge of the historic district. As its name would suggest, the restaurant specializes in seafood, all fresh and all cooked by members of the Withers Moncure family that runs the place.

Entrees range from $4.50 to $7.50 and appetizers from 95 cents to $2.95. For appetizers, one of us had six large clams on the half shell for $2.50 and the other a large crab cocktail for $2.95. For entrees, one had the Captain's Platter, a generous mixture of seafood at $7.50, and the other scallops Norfolk at $7. The entire meal was excellent, topped off by black walnut cake and coconut pie. Only wine and beer are sold. We had a small carafe of wine and coffee and the total cost of the dinner was $22.68, plus tip.

Fredericksburg probably is most famous as the site of some of the worst battles of the Civil War, lying as it did halfway between the Union capital in Washington and the Confederate capital in Richmond. The town was caught in the middle when Union troops attempted to cross the Rappahanock and capture the town in 1862, while Confederate troops shelled them from the heights southwest of town. The battle continued for two days until the Northerners got across, fought through the town and met the opposition beneath the heights. The attacking forces finally were forced back across the river by Confederates firing from behind a stone wall lining Sunken Road.

The visitor center of Fredericksburg and Spotsylvania National Military Park stands there now. We began our Sunday tour at the center, paying 10 cents each for three self-guided tour pamphets. They cover the four sections of the park, Fredericksburg. Chancellorsville, Wilderness and Spotsylvania Court House. Key battlefield areas make up the park, and the National Park Service offers excellent orientation films at Fredericksburg and Chancellorsville. They are different, so see both.

The sites are arranged to be seen in chronological order. Fredericksburg was fought in 1862, Chancellorsville in 1863, Wilderness in early May, 1964, and Spotsylvania Court House mid-May, 1864.

The trouble with visiting battlefields is there generally is not much to see at any one spot. Often it is extremely difficult to visualize the battle that took place, since vegetation growing up in the intervening 100 years often obscures what might once have been an open plain. That has happened to much of the park, but where the battle was especially important, such as Hazel Grove at Chancellorsville and Bloody Angle at Spotsylvania Court House, the sites have been kept generally in the Civil War condition.

Many of the bunkers and trenches the troops dug for battle can still be seen along the driving tours. But most helpful are the paintings the Park Service has erected at key sites, depicting the battles that occurred there.

Keep in mind in touring the four sections that 100,000 men died within the 4,200 acres of parkland during some of the war's bloodiest battles. Among the victims was Stonewall Jackson. By the time of the Wilderness campaign, it was the leaders of the two armies, Grant and Lee, who personally directed the battles over that land. Grant was fighting his way south to capture Richmond. He did a year later and the war ended soon after.

Most of the information you will need about Fredericksburg can be obtained by writing to the Visitor Center, 706 Caroline St., Fredericksburg, Va., 22401, or telephoning (703) 373-9391. For military park information, write National Park Service, Superintendent, Box 679, Fredericksburg.