Jan 6 (Reuters) - A legal battle over whether North Carolina"s new congressional map illegally favors Republicans over Democrats is headed to a panel of judges, one of several lawsuits that could influence who controls Congress after this year"s midterm elections. Lawyers for Democratic voters and advocacy groups told a trio of state Superior Court judges in Raleigh on Thursday that the map, which the Republican-controlled legislature approved in November, effectively deprives Democratic voters of representation by ensuring Republicans will win a majority of seats under almost any circumstance. But a lawyer for Republican lawmakers argued that the redistricting process was legal and transparent, and he contended that courts cannot reasonably determine when partisan considerations have crossed the line. The judges are expected to issue a decision by Tuesday, after the four-day trial concluded on Thursday. Electoral analysts say Republicans would be favored to win at least 10 of the state"s 14 congressional seats under the new map, despite North Carolina"s status as a closely divided swing state. Republicans currently hold eight of 13 districts; the state is gaining a seat as a result of population growth. Republicans need to flip only a handful of seats in the Nov. 8 elections to retake control of the U.S. House of Representatives, where Democrats currently hold a 221-212 edge, including vacancies. U.S. law requires states to redraw their congressional districts every 10 years using data from the U.S. Census to account for population changes. Many states give authority to lawmakers to create the maps, which can lead to gerrymandering, the process by which one political party manipulates district lines to entrench its own power. There are more than a dozen pending lawsuits challenging congressional maps in at least six states including Texas, Ohio and Georgia, according to the Brennan Center for Justice at New York University. The plaintiffs in North Carolina including the North Carolina League of Conservation Voters claim the new map is both racially discriminatory and illegally partisan in violation of the state constitution. The case also involves new maps for state legislative districts. Experts for the plaintiffs testified that the Republican-drawn congressional map was an outlier when compared to thousands of computer-generated maps. "This is the most extreme Republican gerrymander that"s possible," said Elisabeth Theodore, a lawyer for some of the voter plaintiffs, said in her closing argument on Thursday. "This map is deliberately designed to ignore the will of the people expressed through their votes." Phil Strach, an attorney for Republican legislators, argued that any map should be expected to favor Republicans, given that Democratic voters tend to cluster in urban areas. But he also questioned whether courts should even engage in the analysis the plaintiffs were requesting. "What is the line between permissible and impermissible partisan considerations when drawing a map?" he said. "The fact is, that is an unanswerable question." The state Supreme Court moved North Carolina"s scheduled primary election from March to May to allow the case to proceed. Whatever the decision, the case will likely end up in the high court after appeals.