There is gold in Ronald Reagan's words, as dealers and collectors of his handwritten letters and speeches are finding out. In Los Angeles, The Scriptorium already has sold about 30 percent of 114 documents from Reagan's gubernatorial days since putting them on the market a month ago with price tags starting at $350 and going up to $30,000.

Now, in an unusual action for a sitting president, Reagan has written the foreword to a commercial book. This time, though, he is seeing to it that the profits from his words benefit a cause near to his heart -- the Nancy Reagan Drug Abuse Fund -- rather than go into somebody else's pocket.

The foreword is to George Mendoza's "Norman Rockwell's Patriotic Times," a compilation of Rockwell pictures and writings by famous Americans that Viking Penguin Inc. is bringing out next month. If the performance of his seven other Rockwell books can be taken as an indicator -- and advance sales already total 50,000 copies -- Mendoza estimates that royalties could total $500,000.

A longtime fan of Norman Rockwell, Reagan wrote the foreword last year at Camp David, scrubbing a version White House speech writers had written for him. Reagan's 450-word foreword notes that the artist's work "represents a vivid testimony to the greatness of our democracy."

"Our Nation has changed profoundly since the days of the America that Norman Rockwell so skillfully portrayed," the foreword says. "Yet the values that he cherished and celebrated -- love of God and country, hard work, neighborhood, and family -- still give us strength, and will shape our dreams for the decades to come."

In addition to the foreword, Reagan also gave Mendoza, whom he met for the first time Friday, permission to reproduce the painting Rockwell did of him when he was governor. It appears on the book's jacket.

Mendoza says he got the idea for the foreword after a chance meeting last year with a Reagan appointee, then-delegate to UNESCO Jean Gerard, who is now ambassador-designate to Luxembourg.

"We were on a plane bound for Paris and I told her about my eighth Norman Rockwell book. She said, 'You ought to have my friend do the foreword. All you have to do is give 10 percent. He'd be delighted.' I said, 'Who's your friend?'

"And after an hour or so, I said, 'I think, ambassador, that I will give everything,' " Mendoza recalls.

Mendoza says he had an answer back from Reagan within a month after he wrote to him. Later, he said, the White House told him it was the first time a president who was still in office had written the foreword for a commercial book.

It is a point Mendoza's publisher is emphasizing in its prepublication publicity even if the White House is not. Fearful that it might open the floodgates to similar requests, a Reagan aide said it has been a "personal decision" by the president and Mrs. Reagan.

"The nature of the book and the president's interest in Norman Rockwell swung the balance," said the aide. "There are a lot of things that seemingly would fall into the same category, but we can't appear to favor one over another, though we can negotiate terms to prevent exploitation of the president.

"What we don't encourage," the aide continued, "is that presidential appointees go out and get things done this way."

Mendoza said Mrs. Reagan did not know in advance that he had dedicated his book to her as the "spirit behind the flag."

"When she saw it," said Mendoza, "her mouth fell open.