So you still haven't gotten around to visiting Stratford Hall, the Virginia birthplace and early childhood home of Robert E. Lee? The two-hour drive is too much, you say, and what can you do there, anyway?

This Sunday all your excuses run out. It's Coaching Day at Stratford -- a moving feast of horsedrawn carriages on parade and in competition that's held only once every three years.

The parade will begin at 2, but by noon you should have staked out your picnic spot under the flowering dogwood trees that surround the oval lawn in front of the greathouse. Starting at 1, the Virginia Military Institute Band will serenade your picnic.

Heralds stationed in the chimney lookouts of the hall will sound their trumpets to begin the parade. Seventeen carriages, many of them elegantly turned-out coaches pulled by four horses, will sweep down a poplar all,ee and onto the oval. Some of the most top-heavy will be swaying precariously, the polished brasses of the harness gleaming and clanking.

After the parade, there will be competitive drives and exhibitions, giving the drivers a chance to show off the considerable skill required to drive a four-in-hand.

Obstacle driving will be followed by a quick-change exhibition -- a race to see how fast four horses can be unhitched from a coach and four fresh replacements put in their places.

There will also be an exhibition of coach horn-sounding, and a skit called "Going to Ascot," but the real crowd- pleaser is a game called "Tilting the Ring." While the driver keeps his team at an even trot, a lady atop the coach tries to spear a stationary ring suspended from a pole.

Vehicles from Colonial Williamsburg, Maymont Park in Richmond and the Stratford Stables will be on display with those of private owners, and the public will get a chance to inspect them all up close.

But don't let the coaching events monopolize your day at Stratford. Since more than 5,000 people came in 1980, try to avoid the traffic jam by arriving in the morning (the plantation will be open from 9 to 5). Head first for the reception center to see the 18-minute slide show -- an introduction to the Lee family and Stratford Hall. The reception center also offers a museum of memorabilia and a history of the restoration of the house.

Across a connecting bridge is a store that sells, in addition to the usual mementos, flour, grits, barley and meal ground at the plantation's restored mill.

Guides in 18th-century garb lead visitors on a 30-minute tour of the greathouse -- this is a must, even if you miss the dependencies that house the kitchen, schoolhouse and a small archeology museum.

The architecture of Stratford Hall, which was built between 1725 and 1730, is genuinely unclassifiable. The massive brick construction and the setting well back from the Potomac River give the building a fortress-like appearance. Yet its interior layout, with bedrooms on the ground floor and expansive, intricately detailed public rooms above, provides ample evidence of its hospitality. The Great Hall, which connects the two wings of the H-shaped house, is considered one of the loveliest rooms in all of Virginia.

If time permits, stretch your legs by walking the long mile down to the river. The Potomac widens out there and the lookout from the high cliffs above is impressive. COACH FOR A DAY From the Beltway, take Maryland Route 5 south until it joins U.S. 301 at Waldorf. Continue south on 301. Approximately 10 miles after the toll bridge across the Potomac River, take a left onto Virginia Route 3. Go 20 miles and take a left onto Route 214 at Lerty. (Look for a white church on the right and a "76" station on the left.) Follow the signs to Stratford Hall. The admission fee for Coaching Day is $2.50 per adult, 75 cents for children six and older. Armed Service personnel in uniform and children under six are admitted free. For groups of 20 or more in buses, the charge is $1.75 per person. The fee covers the events of Coaching Day and everything that's open on the plantation.