NEW YORK — Online auction giant eBay said Monday it has agreed to acquire PayPal Inc. for roughly $1.5 billion in eBay stock, or 0.39 shares of eBay for each share of PayPal. PayPal is an Internet payment platform, accessible in 38 countries, that derives about 60 percent of its business from eBay. EBay’s own payment service has been losing around $12 million annually. It will be replaced by PayPal, which is projecting pro forma income of 8 cents a share for the second quarter. EBay also previewed results for its second quarter ended June 30, saying it netted $54.3 million, or 19 cents a diluted share, on volume of about $266 million. Sales gains of 48 percent in the U.S. and 148 percent abroad drove eBay’s bottom line. Ebay, with nearly $800 million in cash, will report its full second-quarter results on July 18.