In one sense, it could be reported that Her Britannic Majesty's ambassador to the United Nations, Sir Crispin Tickell, has been serving his French opposite number, ambassador extraordinary and plenipotentiary Pierre-Louis Blanc, weeds for dinner.

From a different viewpoint, the story could be told in terms of a resourceful new British woman chef in New York following to the letter the French culinary instruction: "Use wherever possible the freshest local ingredients.

"For the formal dinner Sir Crispin gave M. Blanc at the British ambassador's official apartment on Fifth Avenue, the ingredients could hardly have been fresher or more local.

The apartment overlooks Central Park-and that is where his chef, Miss Linda Piggott, harvested most of the key ingredients for the dinner.

Newly arrived in New York, Miss Piggott became interested in the foraging tours conducted several days a week by a New York Parks Department ecologist and botanist, "Wildman" Steve Brill. On these tours, Mr. Brill shows his students how to identify and collect scores of varieties of edible vegetables, fruits, berries, herbs and mushrooms in remote areas of Central Park.

The dinner for the French ambassador included lamb covered with a wild black cherry-water mint jam. With this, Miss Piggott served a novel combination of Central Park oyster mushrooms and ringless honey mushrooms.The salad, all from Central Park, comprised wood sorrel, sheep sorrel, lady's thumb and poor man's pepper.

"The French ambassador said it was some of the tastiest food he'd ever eaten-although he found it difficult to believe that the chef was not only not French, but actually English, Mr. Brill reported yesterday.

"The British ambassador found it the best example of Miss Piggott's work since she entered his employ.

"She has followed up the success of the dinner for M. Blanc by serving other "Central Park dinners." They have included chocolate mousse smothered in wine berries, pork marinated with bayberry and sassafras, wild blueberry tart, and ringless honey mushroom soup.

As the harvest continues into the early autumn, the ambassador can look forward to such delights as wild raspberries, strawberries and cherries, more varieties of Central Park mushrooms, rhubarb, and a cornucopia of salads-dandelions, watercress, wild spring onions, spinach and naturally sown carrots and parsnips.