WASHINGTON, April 16 (Reuters) - Inflation in the United States was dormant last month outside a jump in energy costs, while groundbreaking for new homes rebounded with surprising vigor after a big weather-related drop, the government said on Wednesday.

The Consumer Price Index, the most popular gauge of U.S. inflation, rose 0.3 percent last month, the Labor Department said. However, excluding volatile food and energy prices, the CPI was flat -- the tamest reading on so-called core inflation since it was last unchanged in February 1999.

"This is more good news on the inflation front. This is a very, very benign number. It's a sign of price stability," said Richard DeKaser, chief economist at National City Corp. in Cleveland. Economists had expected the CPI to rise 0.4 percent and the core index to edge up 0.2 percent.

A separate report showed housing starts leapt 8.3 percent last month -- the largest gain since September -- to a seasonally adjusted 1.780 million unit annual rate, well above the 1.694 million pace analysts had expected.

"Housing starts remain a bright spot in an economy that otherwise seems to be sputtering," said said Dana Johnson, the head of research at Banc One Capital Markets in Chicago.

Johnson and other analysts said the big jump marked an advance from a February level that had been temporarily depressed by unusually harsh winter weather.