MANCHESTER, England — As Prime Minister Boris Johnson readied the release of his final Brexit plan, politicians and diplomats on Tuesday were puzzling over a basic question: Is he more interested in reaching an agreement with the European Union, or averting blame for failure to get one?

A new proposal from Mr. Johnson is expected on Wednesday, Britain is scheduled to leave the European Union at the end of October, and a deal with the bloc is needed urgently to avoid the risk of a disorderly, possibly chaotic and damaging rupture.

On Tuesday, Mr. Johnson appeared to disown some details of leaked British plans to resolve the central problem, an impasse over the Irish border. But he confirmed enough to suggest that the two sides remain far apart.

Optimists hope that the prime minister will produce an improved offer and that, with the clock ticking toward Oct. 31, an agreement can be clinched in the time-honored tradition of eleventh-hour European negotiations.