Republicans are preparing to cut taxes, slash spending and slow immigration in a broad agenda that will require unifying an unruly party behind dozens of complicated policy choices.

For now, though, they are struggling with a more prosaic decision: whether to cram their policy goals into one bill or split them into two.

It is a seemingly technical question that reveals a fundamental divide among Republicans about whether to prioritize a wide-ranging crackdown on immigration or cutting taxes, previewing what could be months of intramural policy debate.

Some Republicans have argued that they should pass two bills in order to quickly push through legislation focused on immigration at the southern border, a key campaign promise for Mr. Trump and his party’s candidates. But Republicans devoted to lowering taxes have pressed for one mammoth bill to ensure that tax cuts are not left on the cutting-room floor.

President-elect Donald J. Trump met with Republican senators in Washington on Wednesday, as those lawmakers sought clarity on his preferred strategy. He has waffled between the two ideas, prolonging the dispute.

“Whether it’s one bill or two bills, it’s going to get done,” Mr. Trump told reporters after the meeting.

Republicans are planning to ram the partisan fiscal package through the Senate over the opposition of Democrats using a process called reconciliation, which allows them to steer clear of a filibuster and pass bills with a simple majority vote. But for much of this year, Republicans will be working with a one-seat majority in the House and a three-seat majority in the Senate, meaning they will need near unanimity to pass major legislation.

That has left some worried that it will be hard enough passing one bill, much less two.

“There’s serious risk in having multiple bills that have to pass to get your agenda through,” Representative Steve Scalise of Louisiana, the majority leader, said. “When you know you’ve got a lot of people that want this first package, if you only put certain things in the first package, they can vote no on the second and you lose the whole second package. That would be devastating.”

Adding to the urgency of achieving their policy goals, Republicans are facing a political disaster should they fail to deliver. Many of the tax cuts they put into place in 2017, the last time Mr. Trump was president, expire at the end of the year. That means that taxes on most Americans could go up if Congress does not pass a tax bill this year.

Passing tax cuts can take time, though. While much of the Republican tax agenda involves continuing measures the party passed in 2017, Mr. Trump and other Republicans have floated additional ideas, including no taxes on tips and new incentives for corporations to manufacture in the United States. Ideas like that could take months to formulate into workable policy.

Then there is the gigantic cost. The nonpartisan Congressional Budget Office estimates that simply extending the 2017 tax cuts would cost more than $4 trillion over a decade — a price tag that would grow if other tax cuts, like Mr. Trump’s proposal to not tax overtime pay, are included.

Further complicating support for the legislation is that Republicans plan to raise the debt limit through reconciliation, another sensitive issue for fiscal hawks.

Members of the ultraconservative House Freedom Caucus have said they would not support any legislation unless the costs it introduces are offset by spending cuts. While most Republicans support reining in federal spending, agreeing on which federal programs to slash always proves harder than expected. In an attempted workaround, Republicans have instead begun to explore ways to change Washington’s budget rules so the tax cuts are shown to cost less.

The complexity of pulling together a tax bill that can secure the necessary votes has some Republicans hoping to hold off until later in the year and first charge ahead with a smaller bill focused on immigration, energy and military issues. Republicans have not yet publicly sketched out what that bill would look like.

Proponents of that strategy argue it would deliver Mr. Trump an early political victory on immigration and treat a top Republican campaign issue with the urgency it deserves.

“The No. 1 priority is securing our border,” Representative Byron Donalds of Florida told reporters on Tuesday. “In my opinion it’s the top priority, and everything else is a close second.”

Senator Lindsey Graham of South Carolina, the chairman of the Budget Committee who will be overseeing the reconciliation process, has also pressed for a two-bill approach. “If you hold border security hostage to get tax cuts, you’re playing Russian roulette with our national security,” he said.

Republicans have looked to Mr. Trump to intervene and set a clear direction for the party. On Sunday, he wrote on social media that Congress should pass “one powerful Bill,” an apparent victory for lawmakers like Representative Jason Smith of Missouri, the chairman of the House Ways and Means Committee, who had championed that approach. Mr. Trump’s equivocation since then, though, has left Republicans still unsure of which strategy they should pursue.

Mr. Trump’s meeting with top Republican senators on Wednesday will be followed by a discussion with various House Republicans in Florida over the weekend.

In a sign of how politically complicated the tax cut discussion could get, one of the sessions is expected to focus on relaxing the $10,000 limit on the state and local tax deduction, known as SALT.

Republicans included the $10,000 limit in the 2017 tax law as a way to contain the cost of that legislation. But the move angered House Republicans from high-tax states like New York and New Jersey, many of whom voted against the entire 2017 tax bill as a result. Such defections are a luxury that Republican leaders can’t afford this year given their narrow majority.

G.O.P. lawmakers from New York, New Jersey and California could tank a tax bill if they are unsatisfied with how the provision is handled. They are now pushing to lift the cap as part of the party’s tax bill. Eliminating the cap entirely could add roughly $1 trillion to the price tag of the legislation.

Maneuvering ambitious policy agendas through Congress has often been a messy and time-consuming process for presidents. A Republican effort to repeal the Affordable Care Act during Mr. Trump’s first term collapsed after more than six months of discussion.

After quickly passing pandemic relief measures in 2021 under President Biden, much of Democrats’ broader agenda was stymied for almost two years before a second party-line measure passed that was far narrower than many in the party had hoped.

This time around, Republicans will be grappling not only with a historically slim margin in the House, but also a president prone to sudden changes of heart.

“You can argue the merits of both” strategies, said Representative Jodey Arrington, a Texas Republican who leads the House Budget Committee. “He has to tell us what he wants and what he needs.”