A pair of du Ponts named Henry Francis and Pierre Samuel used some of their millions in a pleasingly eccentric way to preserve for us nearly 2,000 acres of history and beauty near the Pennsylvania-/Delaware border.

And those acres are best seen now.

Henry, who collected priceless antiques the way some people collect pennies in a jar, created the Winterthur Museum and Gardens on Rte. 52 north of Wilmington, Del., a 2 1/2-hour drive from Washington. Pierre, who collected land and flower bulbs the way Cousin Henry did antiques, created Longwood Gardens just off the same road across the Pennsylvania line.

Today is the first Sunday of the "spring tour" at Winterthur (pronounced "winter-tour"). Until May 22 visitors can see 30 of the museum's 100 rooms the 60 acres of gardens surrounding the huge former du Pont home.

The museum features furniture, rugs, draperies and art which were used in American homes between 1640 and 1840. Furnishings and even entire rooms and walls were purchased and removed from houses from New Hampshire to Georgia. It is an unbelievably large collection of American furniture and decorative arts.

The main museum, which served as the du Pont living quarters until Henry moved out in 1951 to make his collection available to the public, usually requires reservations one to two months in advance for a weekend visit and costs $12 per person to see both halves. During the spring, $5.50 package tours are offered.

The spring tour includes 16 rooms in the main museum plus the 14 rooms in the South Wing and the garden which are always open without reservation for a price of $2 each.

We visited Winterthur on a rainy Saturday, getting an advance look at the rooms on the spring tour. As in many earlt American homes of the well-to-do, not all the furniture is American-made. One room is furnished entirely in Chinese style and many other rooms have French and English pieces. A tour of the South Wing first and then the main museum carries the visitors through the progressive styles of American furnishings.

By the time we returned to the visitors pavilion (by free jitney which makes the circuit every 10 minutes) the rain had diminished to a drizzle, so we decided to walk through the garden.

Inconspicuous signs identify the plants, and trails meanders through the woods. The Winterthur Gardens are arranged so the plants and flowers are seen in a natural state. Only those that can grow in Delaware are grown at Winterthur.

Longwood Gardens are a bit different. In a four-acre conservatory (greenhouse) on the grounds, it appears its 30 expert gardeners can grow anything.

Pierre vastly expanded the gardens at Longwood after he bought the property from the original owners. He made the purchase after he noticed during a Sunday drive in 1906 that dozens of trees along the road were noticed during a Sunday drive in 1906 that dozens of trees along the road were marked for cutting and decided they should be saved.

Today, in addition to the conservatory which includes a massive organ for occasional concerts, the gardens include a water garden, arboretum, Italian garden, fountain displays, open-air theater, chimes tower, waterfalls and picnic grounds.

Between our Winterthur and Longwood visits, we stayed overnight at the Hotel du Pont in Wilmington, a huge, opulent building which the du Ponts had built more than 60 years ago. Probably because of that association, the hotel is well-maintained and has not been allowed to deteriorate as have many hotels of that vintage.

We ate that evening at Chadda Ford Inn, across the Pennsylvania line, but only nine miles from our hotel. The inn dates from 1736, but no longer offers lodgings. Its menu offers city-type food at city prices, moderate to expensive by Washington standards.

We picked dishes from the upper end of the price range, $7.50 for roast Long Island duck and $8.50 for baked stuffed oysters with crabmeat. The food was excellent and the small, low-ceilinged room features a nice fireplace. but the room was noisy and crowded and smoking was not controlled.

The next day we had the hotel's Sunday brunch buffet in its opulent, darkpaneled Green Room. The buffet table was about 50 feet long and had two chefs standing behind it cooking eggs to order while diners chose their other food. Nearby was a separate table laden with a huge variety of small French pastries. The buffet costs $6.50 per person.

We drove back up to Chadds Ford after checking out, following Rte. 100 up a curving country road along the Brandywine River valley and past more opulence -- huge country estates.

At the junction of U.S. 1 and Chadds Ford Inn again, we turned right onto U.S. 1 and drove a couple hundred yards to the Brandywine Battlefield State Park where one of the key battles of the Revolutionary War took place in September, 1777. George Washington lost it and the chance to spend the following winter in Philadelphia instead of Valley Forge.

The lovely small park includes the headquarters of Washington and Gen. Lafayette, which have been restored and furnished with period pieces. Outside Lafayette's headquarters stands a 300-year-old sycamore tree under which he lay wounded during the battle.

A little south down U.S. 1 is the Brandywine River Museum. Since this is primarily a Wyeth museum in Wyeth country, most of the paintings in the museum are from the Wyeth family -- N.C., Andrew, James and Henriette.

This was an expensive weekend, but when in the land of the opulent, live as the opulents do. It covered about 270 miles and cost about $100 plus gas. The hotel, at $31.50 a night, and the meal at the inn were most of the expense. Add the Winterthur tour price, $2 a head for Longwood Gardens, $1.75 per for the Brandywine Museum, the hotel brunch and tolls if you drive up I-95 to Wilmington.

For Winterthur information (open 10 a.m.-4 p.m. during the spring but closed Mondays) write the museum at Winterthur, Del., 19735 or telephone (302) 656-8591. For Longwood Gardens information (conservatory 10 a.m.-5 p.m. and outdoor gardens 8 a.m. to sunset) write Information Center, Longwood Gardens, Kennett Square, Pa., 19348 or telephone (215) 388-6741. The Brandywine Museum address, 9:30 a.m.-4 p.m. daily, is U.S. Route 1, Chadds Ford, Pa., 19317, phone (215) 459-1900.

For reservations at Chadds Ford Inn, which is closed on Sundays, phone (215) 388-7361. The hotel is at 11th and Market Streets, Wilmington, Del., 19899, phone (302) 656-8121. If you plan to be in the Wilmington area the first full weekend in May, May7 is Wilmington's Garden Day with more than a dozen gardens and houses on view. Write Wilmington Garden Day, Shipley Street at Eighth, 19801, or call St. Andrew's Church (302) 656-6628.