Vacancies in the top jobs in the national security and criminal divisions at the Justice Department are raising concerns among former officials and close observers of the agency.

Lisa Monaco, former assistant attorney general for national security, was named in January to become President Obama’s counterterrorism adviser, and there is no permanent replacement. The head of the criminal division, former assistant attorney general Lanny A. Breuer, left for private practice this month, and his job has no permanent replacement either.

In addition to those critical posts, the Office of Legislative Affairs and Office of Legal Policy have acting heads, and no permanent replacements have been named. Other nominees are in acting positions awaiting Senate confirmation, including Stuart F. Delery to head the civil division and Tony West as associate attorney general, the third-ranking position in the department.

“There is no question that the vacancies always have an effect,” said Robert Raben, an assistant attorney general in the Clinton administration. “Senior leadership matters in policymaking, responsiveness to Congress and making cases.”

Several current and former Justice officials echoed Raben’s comments privately, but they declined to allow their names to be used because they either were not authorized to speak publicly or did not want to anger former colleagues.

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Along with the high-level vacancies, Obama has nominated Assistant Attorney General Thomas E. Perez, who heads the department’s civil rights division, to be the secretary of labor. If Perez is confirmed, another critical vacancy would open in a division that enforces federal statutes prohibiting discrimination.

Obama also has nominated Karol V. Mason to head the Office of Justice Programs, but she, too, is awaiting Senate confirmation. The office provides training and grants to federal, state, local and tribal justice systems. The Office of Public Affairs does not have a permanent director. Former OPA director Tracy Schmaler left last week.

Filling vacancies as a president starts a second term often takes time. But Max Stier, president and chief executive of the nonprofit Partnership for Public Service, described the administration’s transition as “excruciatingly slow.”

“It’s critical to have these positions filled,” Stier said. “It’s very difficult even when there are capable acting or career people in those jobs because the organization just doesn’t operate in the same way. The decisions that have to be made by the senior leadership are enormously challenging and fraught with risk, and it’s very hard for people not confirmed in those top jobs to make the tough calls and to choose solutions that might involve difficult trade-offs.”

Several former officials pointed out that one of Obama’s top priorities, an ambitious gun control agenda, depends on the leadership of the Bureau of Alcohol, Tobacco, Firearms and Explosives. But the Senate has not yet scheduled a confirmation hearing for the president’s nominee for ATF director, B. Todd Jones.

Justice spokeswoman Nanda Chitre said that officials are eager to fill the vacant positions and that department leaders are continuing to bring significant national security and criminal cases.

“The department remains fully committed to fulfilling our most critical missions,” Chitre said. “Particularly in this time of limited budgets, as public servants at every level of the department work hard to serve as sound stewards of taxpayer resources, it’s essential to move forward with a timely confirmation process to fill the remaining vacancies in leadership positions and strengthen our ability to meet future challenges.”

Glenn A. Fine, a former department inspector general, said that Justice attorneys in acting positions usually do a good job.

“But it’s always better to have a confirmed nominee in those positions for stability, longevity and more gravitas within the department and on the Hill,” said Fine, who is practicing law at Dechert LLP.

Administration officials said several candidates are being interviewed for the vacancies. Ann Milgram, a former New Jersey attorney general who is a senior fellow at New York University Law School, is a leading candidate to head the criminal division, according to two people with knowledge of the process.

Filling high-profile vacancies with qualified nominees who aren’t discouraged by the sometimes-arduous confirmation process is difficult, current and former officials said.

“The search for talented people who are willing to go through the modern confirmation process and who are experienced and are diverse is no joke,” Raben said. “It’s hard, it’s really hard.”