By Lucia MutikaniWASHINGTON, July 30 (Reuters) - U.S. economic growth slowed in the second quarter as imports widened the trade deficit, but robust consumer spending and business investment related to the buildout of artificial intelligence infrastructure underscored strong domestic demand. "Underlying growth was solid, but is unlikely to be sustained," said Oliver Allen, senior U.S. economist at Pantheon Macroeconomics. Gross domestic product increased at a 1.5% annualized rate last quarter, the Commerce Department's Bureau of Economic Analysis said in its advance estimate of second-quarter GDP. In addition to larger tax refunds, spending was boosted by higher-income households that are benefiting from strong growth ⁠in asset prices. The recently ended FIFA World Cup tournament also likely added to the strength as did midterm election-related spending by nonprofits.