By Colleen Jenkins

WINSTON-SALEM N.C. (Reuters) - A federal judge will be asked on Monday to block key provisions of North Carolina's overhauled voter law, including fewer early voting days and the elimination of same-day registration, from remaining in effect for November's midterm elections.

The groups challenging the law argue the court needs to act ahead of a full trial next year to ensure no eligible voters, particularly African Americans, are denied or restricted of their right to cast a ballot.

Attorneys for the state have countered that some of the electoral changes were in place for the primary election in North Carolina in May and results showed no disproportionate hardships being imposed on minority voters.

North Carolina is among several states forced to defend changes to voting protocol, including whether requiring voters to show photo identification is constitutional. Judges have handed a string of victories to challengers in recent months, overturning voter ID laws in Pennsylvania, Wisconsin and Arkansas.

The photo ID requirement adopted last year by North Carolina's Republican-led legislature takes effect in 2016. But critics say it already has caused confusion and want election workers barred from discussing it at the polls this fall.

Challengers also will ask U.S. District Judge Thom Schroeder in Winston-Salem this week to put on hold parts of the law that shorten the early voting period by seven days, ban same-day registration and end a program allowing 16- and 17-year-olds to pre-register to vote.

The changes were designed to discourage minority voters, who typically vote Democratic, from going to the polls, argue groups including the National Association for the Advancement of Colored People and the American Civil Liberties Union and the U.S. Justice Department.

"We want to be sure that these voters' stories are heard now because so much is at stake if the law is not stopped," said Advancement Project voting rights attorney Penda Hair.

Lawyers for North Carolina said fears of lower participation by minorities or longer lines at polls proved unfounded during the primary election in May. The challenged provisions were in effect, with the exception of the photo ID requirement, which supporters say is needed to combat voter fraud.

"In this case, there can be no discriminatory effect on African American voters, or other minority groups because the challenged provisions ... apply equally to all voters regardless of race," attorneys for the state said in court briefs.

(Reporting by Colleen Jenkins; Editing by Bill Trott)