By Adam Rose BEIJING (Reuters) – China's economy grew at its slowest pace in 18 months in the first quarter of 2014, official data showed on Wednesday, with signs of waning momentum already prompting limited government action to steady the world's second-largest economy. Authorities have ruled out major stimulus to fight short-term dips in growth, and some analysts think the economy will continue to lose momentum into the middle of the year. It was China's slowest annual growth since the third quarter of 2012, when growth was also 7.4 percent. "I don't think they're going to announce any further significant measures to support growth." Beijing has announced some modest measures, such as tax cuts for small firms and speeding up some investment in rail projects, to try to steady growth around its target of 7.5 percent without disrupting plans to restructure the economy.