WASHINGTON — Speaker Paul D. Ryan, hoping to revive his dream of rewriting the tax code, will insist in a speech on Tuesday that Republicans come together to avoid letting a “once in a generation” opportunity slip out of their hands.

A year after Mr. Ryan unveiled a blueprint called “a better way” for overhauling the tax system, his party has struggled to come together around a plan. The tax overhaul has stalled amid the legislative logjam Republicans have created in trying to repeal and replace the Affordable Care Act. The tax cuts they have promised might languish until 2018 — if they happen at all.

In his first major speech on the subject this year, Mr. Ryan will tell Republicans they must move forward without further delay. “We need to get this done in 2017,” he will say to the National Association of Manufacturers in Washington, according to excerpts from his speech. “We cannot let this once-in-a-generation moment slip.”

According to his office, Mr. Ryan will not go into great detail about where he stands on the various tax proposals that have been dividing Republicans for months, but he will provide a broad outline of his thinking.