WASHINGTON  Senator Barack Obama emerged from Tuesday’s primaries leading Senator Hillary Rodham Clinton by more than 100 delegates, a small but significant advantage that Democrats said would be difficult for Mrs. Clinton to make up in the remaining contests in the presidential nomination battle.

Neither candidate is expected to win the 2,025 pledged delegates needed to claim the nomination by the time the voting ends in June. But Mr. Obama’s campaign began making a case in earnest on Wednesday that if he maintained his edge in delegates won in primaries and caucuses, he would have the strongest claim to the backing of the 796 elected Democrats and party leaders known as superdelegates who are free to vote as they choose and who now stand to determine the outcome.

Mrs. Clinton’s aides said she could still pull out a victory with victories in the biggest primaries still to come, including Ohio and Texas next month. But Mr. Obama’s clear lead in delegates allocated by the votes in nominating contests is one of a number of challenges facing her after a string of defeats in which Mr. Obama not only ran up big popular vote margins but also made inroads among the types of voters she had most been counting on, including women and lower-income people.

Should the cracks in her support among those groups show up in Ohio and Texas as well, it could undermine her hopes that those states will halt Mr. Obama’s momentum and allow her to claim dominance in many of the biggest primary battlegrounds.