The arrangement is a striking departure for Mr. Cruz, who has in the past rebuffed calls from some Republican leaders — including members of the Kasich campaign and Mitt Romney, the 2012 Republican nominee — to divvy up states in an effort to complicate Mr. Trump’s path.

The move also signals a major shift in tone from the Cruz campaign toward Mr. Kasich, whom Cruz aides have long cast as a spoiler in the race. Mr. Cruz has openly questioned whether Mr. Kasich was auditioning to be Mr. Trump’s vice president.

But Indiana, which votes on May 3, is seen as critical to Mr. Cruz’s chances of keeping Mr. Trump safely beneath the delegate count required for the nomination. In a signal of Indiana’s importance, Mr. Cruz has held several events in the state in recent days, giving relatively little attention to the five states that vote on Tuesday, when he is expected to lose more delegates to Mr. Trump.

Mr. Kasich’s team had hoped to coordinate in this manner much sooner. Last month, at a debate in Miami, Mr. Weaver broached the possibility with Mr. Roe of splitting the remaining states in an effort to minimize Mr. Trump’s delegate haul. Mr. Cruz’s team rejected the overture, in part because it would have meant ceding the spotlight in high-profile contests, such as New York, in the Northeast and mid-Atlantic states. Mr. Weaver and Mr. Roe reached the accord this time and the two candidates did not discuss it, according to an adviser to Mr. Kasich.