WASHINGTON — Lawmakers are ready to question the ousted head of the Internal Revenue Service as Congress holds its first hearing on the tougher scrutiny the IRS gave tea party and other conservative groups that applied for tax-exempt status.

With the scandal joining the parade of political headaches buffeting President Barack Obama, the Republican-run House Ways and Means Committee planned to question the agency’s ousted chief, Steven Miller, today.

Miller, acting director until he resigned Wednesday, seems sure to get a hostile reception from the committee. Members of both parties have spent the past week bitterly chastising the agency for abandoning its charge of making nonpolitical decisions about which groups should qualify for tax-exempt status, which makes it easier for them to collect contributions from donors.

Lawmakers also have said that despite asking the IRS repeatedly about complaints from conservative groups that their applications were being treated unfairly, the agency — including Miller — never told them the groups were being targeted, even after May 2012, when the agency said Miller was briefed on the practice. Miller was previously a deputy commissioner whose portfolio included the unit that made decisions about tax-exempt status.

Also testifying today was J. Russell George, the Treasury Department’s inspector general for tax administration.

A report George issued this week concluded that the IRS office in Cincinnati, which screened applications for the tax exemptions, improperly singled out tea party and other conservative groups for tougher treatment. The report says the practice began in March 2010 and lasted more than 18 months.

Republicans have spent the past few days trying to link the IRS’ improper scrutiny of conservatives to Obama. The president has said he didn’t know about the targeting until last week, when Lois Lerner, who heads the IRS division that oversees tax-exempt groups, acknowledged at a legal conference conservative groups had been singled out. She said it was wrong and apologized.

“I promise you this, that the minute I found out about it, then my main focus was making sure that we get the thing fixed,” Obama said Thursday.

Even so, less than four months into his second term, the president has been on the defensive for the IRS controversy, along with questions about last September’s attack in Benghazi, Libya, that killed the U.S. ambassador and three other Americans.

In one of the latest GOP attacks, Sen. Rob Portman, R-Ohio, wrote Obama on Thursday asking whether the White House or Treasury Department pressured the IRS on the treatment of conservative groups. In the letter, Portman accused the administration of “policies that threaten to chill disfavored political speech.”