A federal judge has said he will wait until at least Sept. 19 to decide whether to prohibit a Maryland state contractor from cutting down mature trees on the Georgetown Branch Trail until a lawsuit opposing the Purple Line’s construction is resolved.

U.S. District Judge Richard J. Leon said he needs time to determine whether he has jurisdiction in the case and whether a tree-cutting ban would “effectively be undercutting” an appeals court that allowed the state to begin building the light-rail line in the trail corridor while it considers the lawsuit.

The state’s contractor, Purple Line Transit Partners, closed the three-mile wooded recreational trail between downtown Bethesda and Silver Spring last week. Workers immediately started clearing underbrush and cutting down trees less than nine inches in diameter to install fencing, which has been allowed to continue.

A lawyer for the Maryland Department of Transportation told Leon in a court filing Thursday that the state had planned to begin cutting all trees Sept. 18. Pushing back that date would result in a two-week delay and cost the state $6.1 million, but the contractor could hold off on clearing larger trees until Sept. 20, according to the filing. Leon is scheduled to hold a hearing Sept. 19 on Purple Line opponents’ request to ban all tree cutting until their 2014 lawsuit is resolved.

The opponents have argued that allowing trees to be cut down before the court case is decided would cause irreparable environmental damage.

The state is appealing Leon’s previous ruling that would require transit agencies to reopen the project’s federally required environmental review — a process that could take months — to consider what impacts Metro’s declining ridership could have on the Purple Line’s ridership. State officials have said Metro’s ridership would have no significant impact.

The 16-mile Purple Line would run between Bethesda in Montgomery and New Carrollton in Prince George’s County.