“I am not the president’s lawyer,” Mr. Garland is expected to say, according to excerpts of his planned remarks. “I will also add that I am not Congress’s prosecutor. The Justice Department works for the American people.”

It will be Mr. Garland’s first appearance before the committee since the special counsel, Jack Smith, brought two criminal indictments against former President Donald J. Trump and a plea deal for Hunter Biden collapsed.

Mr. Garland, circumspect and soft-spoken, is taking a more aggressive approach than during past hearings. In his prepared remarks, he also denounces escalating threats against prosecutors — including Mr. Smith — and F.B.I. agents by Trump supporters, which have prompted significant increases in security.

It is “dangerous,” he is expected to say. “We will not be intimidated. We will do our jobs free from outside interference. And we will not back down from defending our democracy.”

Republican committee members have signaled that they intend to grill Mr. Garland, a by-the-book former prosecutor and federal judge, about his role in the later stages of a five-year investigation into Hunter Biden. It appeared to be nearing an end this summer until it imploded in July over the terms of the plea deal between Mr. Biden and the U.S. attorney for Delaware, David C. Weiss.

They are expected to focus, in particular, on a claim by a former Internal Revenue Service investigator, Gary Shapley, who said Mr. Weiss had suggested that he was being blocked from fully investigating the case of Mr. Biden’s taxes by being denied the power to independently pursue charges in jurisdictions outside Delaware.

Mr. Weiss forcefully denied the charge, and several other officials also rebutted the claim.

“He has been advised that he should get anything he needs,” Mr. Garland said of his interactions with Mr. Weiss during testimony before a Senate committee in March.

Mr. Garland is also likely to be questioned about his initial reluctance to name Mr. Weiss as special counsel in the matter, particularly his claim that such an appointment would not grant Mr. Weiss any additional authority to investigate tax charges in other jurisdictions. Mr. Garland eventually granted that designation in August at the request of Mr. Weiss.

The theory that President Biden intervened to protect his son, widely trumpeted by House Republicans and amplified by conservative news media, is central to the impeachment inquiry begun by Speaker Kevin McCarthy under pressure from the right flank of his party.

Republicans see Mr. Garland as a critical link even though he has taken steps to insulate himself from the case, including by reappointing Mr. Weiss, a Trump appointee. Similarly, officials say, he has virtually cut off communications with the White House since the department began investigating Mr. Trump.

The committee is also expected to focus on the multiple indictments of Mr. Trump, including over his efforts to subvert the results of the 2020 election. Representative Jim Jordan, Republican of Ohio and the chairman of the Judiciary Committee, has pointed to these as further evidence of the department’s weaponization under Mr. Garland.

It is not Mr. Garland’s first appearance before lawmakers this year. In March, he faced four hours of blistering questioning by the Senate Judiciary Committee.

One by one, Republicans accused Mr. Garland of politicizing the department by aggressively investigating Republicans and conservative activists while shielding Democrats. They rebuked him over a range of policy and law enforcement issues, including his response to the fentanyl and immigration crises as well as the Supreme Court’s decision to end the constitutional right to an abortion.

The stakes are considerably higher this time.

Over the past week, Mr. Jordan has increased the pace and scope of his demand for access to documents and officials, including Mr. Weiss and his deputies, claiming they are fundamentally necessary for his committee to fulfill its oversight function.

The department has refused to comply, citing laws and regulations that prevent it from disclosing details of open investigations.

Mr. Jordan’s ultimate goal, officials believe, is to add an obstruction-related article to Mr. Biden’s impeachment — or to justify an independent effort to impeach Mr. Garland, they said.