There's no party like a boating party, and the Potomac offers many possibilities for entertainment alfoat. You can charter a dinner cruise or borrow a yact and a skipper, and sail off into the sunset as far as your wallet will carry you.

On a starry summer night aboard a gaily lit boat, you glide past the Kennedy Center, the Lincoln Memorial and the shorelines of Virginia and Maryland and see the same old city from a new perspective.

Round up the gang and charter a dinner cruise on the Dutch-style tour boat owned by Washington Boat Lines. The Spirit of '76, a 65-footer, operates between Georgetown and the Lincoln Memorial, It will hold 50 to 60 for a sitdown dinner; 85 for a buffet dinner or cocktail party; and 100 passengers for a cocktail party. The operators provide beverages, for an extra cost, and will work with your caterer. Depending on the number of guests, dancing can be arranged. A three-hour cruise is $600 to $900, depending upon the day of the week.

If you've generated more enthusiasm than the Spirit of '76 can accommodate, check into charters on the Diplomat, the 125-foot cruise ship that plies the river between Maine Avenue and Mount Vernon. It's also owned by Washington Boat Lines. With space reserved on the upper deck for dancing, this vessel can handle 275 to 300 for a stand-up party. For dinner, 150 can sit down, and a tape system on board supplies the music. Or you can hire your own band.

Charter fees for a minimum three-hour cruise are $1,200 to $2,000 depending on the day of the week. Beverage service available.

Either boat can be elegant or informal, for a reception, a fund raiser, a company outing, a class reunion or a wedding.

By maybe you're just a party of two. There are always the regular sightseeing trips on the Diplomat and the Spirit of '79. For a recorded schedule, call 554-8000.

At the Gangplank Marina, there are three smaller boats to charter for basking in the sun or entertaining clients. The boats are complete with captain and crew, so you really can take it easy.

A party of six or fewer can charter a 45-foot Columbia motor sailer for about $10 an hour per person. Or, there's a 45-foot Hatteras motor yact also for six or fewer at $10 an hour per person. Or, if you've always wanted to indulge an urge to play J.P. Morgan, an 87-foot luxury motor yacht is available for $175 an hour. This vessel will accommodate 24 for cocktails and 14 for a sitdown dinner -- just the size for your board of directors. Food and beverages are extra.

Aside from the power boats, there is a 22-foot weekender sloop, bare-bones style, which can be rented for $40 for five hours or $70 for 10 hours. You've got to demonstrate your sailing ability to take this baby out. Weekend rates are $130 for Saturday morning to Sunday evening and $150 from Friday enening to Sunday evening. The boat sleeps five, has cooking facilities and a head. Bring your own food and bed linens.

Over in Old Town Alexandria, Potomac Party Cruises, at the foot of Prince Street, has a 60-foot boat, the Mary Ann, available for charter. It accommodates 48 and carries a crew on three.

The charter fee is $150 an hour. Arrangements can be made to have dinner served on board at an extra charge, or cater your own. Phone: 683-6076.

Forty-five minutes away at Harrington Harbor in Friendship, Maryland, there's a 51-year-old all-wood motor yact named the "Sakonnet." Her owner, Dan Wilson, describes her as having "tons of charm." She's a 75-foot luxury yacht with yards of gleaming mahogany and she can hold 20 to 25 people. Charter fees are $140 an hour. For those eager to spend more than an hour on the Chesapeake Bay aboard the "Sakonnet," package deals are available; they start at six hours for $100 an hour. To arrange a charter, contact Dan Wilson at 554-3343.