ComScore says Samsung edged out Motorola by a fraction of a percent to take top place in the U.S. handset market in the first quarter of 2010.

Competition between Motorola, Samsung and LG remains fierce, with each company’s U.S. market share separated by just fractions of percentage points.

Samsung has slightly more market share than Motorola, whose portion of the U.S. market fell 1.6 percentage points to 21.9 percent in the first quarter. LG lost one-tenth of a percent to come in at 21.8 percent of the U.S. market.

BlackBerry-maker Research In Motion (RIM) gained 1.3 percentage points to reach 8.3 percent of the U.S. market, edging slightly ahead of Nokia, which lost nine-tenths of a percentage point in the first quarter.

ComScore also said AT&T and Tracfone were the only top five operators to gain market share in the first quarter, with AT&T gaining two-tenths of a percentage point and Tracfone gaining three-tenths of a percentage point. Verizon, Sprint and T-Mobile USA all lost one-tenth of a percentage point.

Overall, Verizon maintained its lead with 31.1 percent of the U.S. market while AT&T came in second with 25.2 percent. Sprint squeaked past T-Mobile to keep the number three spot, though the companies are in a dead heat with each having about 12 percent of the U.S. market. Tracfone now has a 5.1 percent market share.