As she cruised down the Potomac River to Mt. Vernon yesterday afternoon, Marion Javits said that Washington is chaning. "It's better. The new people are raffish and doing their own thing; but the're being innovative."

The wife of the ranking Republican on the Senate Foreign Relations Committee and 20 other Senate wives were guests of Rosalyn Carter aboard a Wilson Line tour ship along with the wives of the delegates to the signing of the Panama Canal treaties. They lunched American - avocado stuffed with Maryland crabmeat, Jamestown ham, Virginia fried apples and beaten biscuits - aboard a catamaran which had been turned into a reasonable facsimile of a silk purse by the White House.

The linoleum had been covered with green carpeting; the ship's railing garlanded with 2,000 feet of laurel, pink and red geraniums.

Tables for eight were covered with hot-pink cloths and overlays of apple green. Green and geraniums filled the silver basket centerpieces and the hanging baskets at each window.

Marion Javits, who was also at the White House dinner Wednesday night, spends most of her time in New York, a fact often commented on in the press. She said, "The press never notices when I'm here for a long time. I've been here all week with my little family."

"I had a marvelous time last night. I was seated between Trudeau and Kissinger. It was so funny. At the same table there was a fascinating Mexican psychoanalyst. It was a wonderful table. Somebody out there must like me."