SAN FRANCISCO — Activist investor Carl Icahn is retreating from his battle with Apple’s board of directors, ending a high-profile campaign to pressure the iPhone maker into spending more money to buy back its own stock.

The about-face outlined in an Icahn letter to Apple’s shareholders figures to turn the company’s Feb. 28 annual meeting into a more sedate affair.

Icahn had been trying to drum up support for a non-binding proposal urging Apple Inc. to spend at least $50 billion buying back its shares during the fiscal year ending in September.

The idea faced mounting opposition from other stockholders who supported the company’s board.

To hit Icahn’s target, Apple’s board would have had to increase the volume of stock buybacks authorized under a program unveiled last year. That plan allows Apple to spend $60 billion on its stock through December 2015. The company only had $37 billion still left for stock purchases under that plan as it began the fiscal year.

That means the board would have had to expand the stock repurchase program to placate Icahn, an irascible billionaire who has a long history of pestering companies to embrace his ideas after buying large stakes in them. Icahn began buying Apple stock about six months ago and has said he owns more than $3 billion worth of the shares. His holdings translate to a stake of less than 1 percent.

Apple previously has said it remains committed to making sensible use of the nearly $159 billion in cash that it held at the end of December.

Apple CEO Tim Cook said the company spent $14 billion buying back stock in the past two weeks. Shares had dropped 8 percent following a quarterly earnings report that disappointed Wall Street.