NEW YORK--Former White House spokesman Larry Speakes quit as chief spokesman for Merrill Lynch & Co. yesterday, days after he created an uproar by admitting he twice changed President Reagan's quotes in relating them to the press.

Speakes said in a statement that his resignation was "the best course of action for Merrill Lynch and for me personally. Merrill Lynch is a great firm and the industry leader, and I've enjoyed being part of it."

The announcement reflected intense pressure on Speakes to resign as head of communications at the Wall Street investment giant because of disclosures in his forthcoming book on his tenure as White House spokesman. In the book he said he had attributed to Reagan comments the president never made.

Merrill Lynch said in a statement: "We accept Larry Speakes' resignation with regret. Larry has made a signficant contribution to our firm during his time here, and we wish him well in every regard."

Company spokesman Fred Yager declined to elaborate on Speakes' resignation.

But a knowledgeable source said senior Merrill Lynch management wanted Speakes to quit because the disclosures raised serious questions about his credibility and, by extension, that of the company.

Speakes joined Merrill Lynch with much fanfare 14 months ago. Sources inside the firm said he earned between $200,000 and $250,000 a year.

Reagan, leaving Washington for a weekend at Camp David, Maryland, declined to answer reporters' questions about Speakes.

The resignation was announced after Speakes scrapped plans to attend a White House Correspondents' Association dinner in Washington next week as guest of the Washington Post. Earlier he cancelled an appearance at Denison University in Granville, Ohio, because of what school officials called the controversy over his new book, titled "Speaking Out."

In his book, Speakes says that after the Soviet Union's downing of a Korean Air Lines passenger jet in 1983, he quoted Reagan as saying the incident illustrated a "Soviet versus the world problem," and not antagonism between the superpowers. Speakes' book said that comment really came from Secretary of State George Shultz.

Speakes said he also credited Reagan with some of Shultz's suggestions for possible retaliatory measures.

In the other instance, Speakes says he quoted Reagan as telling Soviet leader Mikhail S. Gorbachev during their Geneva summit meeting, "There is much that divides us, but I believe the world breathes easier because we are talking here together."

He said in the book that he and a press aide, Mark Weinberg, concocted the comment.