NEW YORK, June 25 (Reuters) - U.S. natural gas futures lost ground on Tuesday for a fourth straight session, with the front contract pressured to a 3-1/2-month low by milder weather forecasts for later this week and next week that should slow demand. Front-month gas futures have lost nearly 6 percent in the previous three trading sessions amid signs that the extended weather outlook was trending milder. It was the biggest three-day slide for the near month in seven weeks. "Gas is down on the cooler six-to-10-day weather forecast," a Texas-based trader said. At 10 a.m. EDT (1400 GMT), front-month July gas futures on the New York Mercantile Exchange, which expire on Wednesday, were down 4.3 cents, or 1.2 percent, at $3.696 per million British thermal units after slipping to $3.685, the lowest for the nearby contract since mid-March. The front month eked out a small gain last week, its first after sinking 12 percent in the previous three weeks, but many traders remained skeptical of the upside without a sustained, broad-based heat wave, particularly with inventories comfortable and gas production still flowing at or near a record high. Early cash quotes for Wednesday delivery at Henry Hub , the benchmark supply point in Louisiana, were down 4 cents at $3.77 on light volume of about 245 million cubic feet. Early Hub differentials firmed slightly to about 6 cents over NYMEX, from a 4-cent premium on Monday. Prices on Transco pipeline at the New York citygate jumped 21 cents to $4.50 on the early-week heat. Volume was moderate at about 150 mmcf. While heat is forecast to continue in the West for the next two weeks, MDA Weather Services expects near seasonal or below seasonal temperatures to dominate the eastern half of the nation during the six-to-15-day time frame. The Baker Hughes gas drilling rig count fell to another 18-year low last week, but U.S. gas production has not slowed much, if at all, this year. The Energy

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