The city’s Fire Department is being forced to explain its reliance on a written test in deciding whom to hire after the Justice Department filed a lawsuit claiming the test is limiting the number of minorities on the payroll.

Filed in U.S. District Court in Brooklyn yesterday, the suit comes in the wake of several efforts by the Fire Department and the city to boost the number of black and Hispanic firefighters. About 3% of the city’s 11,000 firefighters are black and 4.4% are Hispanic, according to the civil complaint.

The lawsuit focuses on two written exams taken by recent classes of prospective firefighters. The exams are from 1999 and 2002. An applicant’s score on the written exam and a physical test provide the basis for the department’s hiring decisions.

The complaint, brought under Title VII of the Civil Rights Act of 1964, describes this system as “an open competitive examination process” that has “resulted in a disparate impact upon black and Hispanic applicants.” The test, the complaint said, is not “job-related for the position in question.”

“Municipal employers may not use written tests that are not job related and that make it more difficult for black and Hispanic applicants to become firefighters,” the U.S. attorney in Brooklyn, Roslynn Mauskopf, said in a statement sent via e-mail. The assistant attorney general for civil rights, Wan Kim, said in a statement sent via e-mail that the city’s testing practices were “disproportionately screening out large numbers of qualified” minority candidates.

White candidates passed the 2002 exam at a rate of 97.2%, while the pass rate for black candidates was 85.6%, the complaint said. Hispanic candidates passed 92.8% of the time.

The complaint said blacks and Hispanics “are under-represented among the higher-scoring applicants on the eligibility list, and over-represented among the lower-scoring applicants.”

The city and the Justice Department declined to release a copy of the exams, which are multiple choice, yesterday. Practice exam questions from several years ago include math problems relating to how heavy a load a certain diameter of rope could lift, and questions relating to the most important type of information to include in a report on a fire.

It is not the first time the federal government has gone to court over the number of minorities in the fire department. For a brief time in the 1970s, the fire department was required under a federal court order to hire one black or Hispanic applicant for every three white candidates hired, a lawyer for the Center for Constitutional Rights, Shayana Kadidal, said yesterday. The group filed a complaint with the Equal Employment Opportunity Commission that resulted in yesterday’s lawsuit.

Last August, Mayor Bloomberg said the fire department would no longer require applicants to complete college coursework. This change, Mr. Bloomberg said, was part of an effort to increase diversity.

The last city audit of the fire department’s recruitment program found that the department “undertook a number of efforts to attract women and minority candidates” to take the firefighter exam. According to the 2000 audit by the city’s Equal Employment Practices Commission, those steps included placing English- and Spanish-language advertisements in “minority-oriented newspapers,” conducting a phone-a-thon reaching out to women, and making the exam application more accessible.

The firefighter exam is generally given every four years. The 2007 exam, already administered, is not part of the suit.

A city lawyer, Georgia Pestana, said in a statement sent via e-mail that “as everyone except the Department of Justice seems to know, NYC has the most celebrated, best trained and most capable Fire Department in the country.”

The lawsuit, Ms. Pestana said, focused on “old written exams,” and “will do nothing to increase Fire Department diversity.”