* Gas-directed rig count slides, first drop in 3 weeks * Horizontal rigs slip, match 20-month low from early April * Oil rig count climbs for fourth time in 5 weeks NEW YORK, April 26 (Reuters) - The number of rigs drilling for natural gas in the United States fell this week to the lowest since May 1999, as producers continued to pull back from dry gas drilling despite recent prices gains. The gas-directed rig count, which had gained slightly in two previous weeks, slid by 13 this week to 366, data from Houston-based Baker Hughes showed on Friday. Producers have mostly been curbing dry-gas drilling in favor of more profitable oil and liquids-rich plays such as Eagle Ford in Texas and Marcellus in Appalachia. But a 40 percent run-up in spot gas prices since mid-February to a 21-month high of $4.429 per million British thermal units just last week, had stirred concerns that gas output, still flowing at or near record highs, could increase in coming weeks. The oil-focused rig count rose by 10 to 1,381, its fourth gain in five weeks, Baker Hughes data showed. The oil count is up 53 rigs, or 4 percent, from the same week last year. Baker Hughes also reported that horizontal rigs, the type often used to extract oil or gas from shale, fell by 13 this week to 1,084, matching the 20-month low of 1,084 posted three weeks ago. The horizontal count is down 9 percent from the record high of 1,193 set last May. Drilling for natural gas has mostly been in decline for the last 18 months. The count is down about 61 percent since peaking in 2011 at 936, but so far production has not slowed much, if at all, from the record high hit last year. The associated gas produced from more profitable shale oil and shale gas liquids wells has kept dry gas flowing at a brisk rate. The U.S. Energy Information Administration expects marketed gas production to edge up slightly in 2013 to its third straight yearly record. Gas futures prices, which were down about 6 cents in the $4.10 area just before the Baker Hughes data was released, climbed about a penny after the report.