NEW YORK — U.S. stocks pulled further back from their records on Friday to cap the weakest week for the S&P 500 since May.Indexes sloshed between small gains and losses for much of the day before turning lower in the afternoon after Iran said it seized a British oil tanker, the latest escalation of tensions between Tehran and the West. Reined-in expectations for how deeply the Federal Reserve will cut interest rates at its next meeting also weighed on stocks.The S&P 500 fell 18.50 points, or 0.6 percent, to 2,976.61. After setting its record high on Monday, the index see-sawed mostly lower and lost 1.2 percent for the week. It’s just the second down week for the index in the last seven.The Dow Jones Industrial Average fell 68.77, or 0.3 percent, to 27,154.20, and the Nasdaq composite lost 60.75, or 0.7 percent, to 8,146.49.Momentum for stocks has slowed since early June, when they began soaring on expectations that the Federal Reserve will cut interest rates for the first time in a decade to ensure the U.S. economy doesn’t succumb to weaknesses abroad. The Fed’s next meeting is scheduled for the end of this month.Late Thursday, Treasury yields sank after comments by Fed officials raised expectations that it may cut rates by half a percentage point, rather than the typical quarter point. But yields climbed Friday as the market grew more convinced that the Fed will cut just 0.25 percentage point on July 31.