NEW YORK — Stocks rose again Monday, led by gains in retailers and smaller companies after a report showed strong orders last month for service-sector companies, where most Americans work. Investors were also encouraged by the resumption of trade talks between the U.S. and China.That helped stocks build on the huge gains they made Friday. The U.S. economy has been a top concern for investors over the last three months, and the strong report on service companies showed that banks, health care and construction companies were holding up well.Dollar stores and other retailers, clothing companies and car makers all climbed. Amazon surpassed Microsoft to become the most valuable publicly-traded company. The two-day gain followed a huge pullback last Thursday, when a weak report on manufacturing helped send large multinational companies sharply lower.“The portion of the economy that’s domestically focused is doing better than the portion that is exporting, and arguably that is coming from the trade winds and the tensions we see from that,” said Jason Pride, chief investment officer of private clients at Glenmede.The S&P 500 added 17.75 points, or 0.7 percent, to 2,549.69. The index, a benchmark for many mutual funds, closed at its highest in more than three weeks, and it’s risen 8.4 percent since Dec. 24. It’s still 13 percent below the record high it reached late September.