Three-quarters of eighth-graders in New York City’s public schools cannot write proficiently, a problem demonstrated by more than two-thirds of students statewide, according to results from a federally administered test released yesterday.

The National Assessment of Educational Progress, known as the Nation’s Report Card, found that 55% of city eighth-graders scored at the basic level, meaning they had a partial mastery of skills, and 20% scored below basic. The national average was 57% scoring at basic and 13% scoring below. The New York State scores represent no significant progress since the last time the test was administered, in 2002. Nationally, eighth-graders made modest but significant gains, with the average score rising three points since 2002, though the percentage of students scoring proficient, 33%, did not change significantly.

There is no way to record change over time for New York City, because 2007 was the first year the test results were separated out from state scores.

The city’s scores can be compared with other large central cities. By that metric, New York City’s scores were statistically neither better nor worse than the average; they were lower than three cities that topped the average: Charlotte, N.C.; San Diego, Calif., and Austin, Texas.

The director of research at the Foundation for Education Reform and Accountability, Jason Brooks, released a statement comparing the NAEP results to results produced by New York State tests, which last year showed eighth-graders posting large improvements on a reading test, with 42% meeting state standards versus 37% the year before.

Mr. Brooks said the discrepancies prove state exams are “dumbed-down.”

A spokesman for the city Department of Education, David Cantor, pointed out that the writing scores are higher than the levels the city’s eighth-graders posted on national reading and math tests last year. On the 2007 reading exam, 19% of eighth-graders scored proficient, and 16% did so on the math.

Mr. Cantor also pointed to the city’s parity with other large central cities. “Nevertheless,” he said, “the message from today’s results is clear: Like the rest of the country, we have a lot more work to do in teaching our middle-school students to write.”

Nationwide, some achievement gaps were closed, with black students in large central cities posting gains of eight scale score points since 2002 and Hispanic students posting gains of seven points, according to the Council of the Great City Schools.

A national education advocacy group, the Education Trust, said in a statement that New York State’s Hispanic students’ scores have risen by at least 15 points since 1998.

In New York City, the report shows both gender and racial achievement gaps, with female eighth-graders outperforming males on average by 20 points; white students outperforming blacks by 27 points, and whites outperforming Hispanic students by 30 points.

There was also a gap along income lines, with students who receive free and reduced-price lunches scoring on average 23 points below students who do not. In the past, New York City’s results on NAEP exams have come under question because of the percentage of city students who are tested with accommodations — those who are nonnative English speakers and students with disabilities are eligible for accommodations.

On the writing test, 19% of New York City eighth-graders were tested with accommodations, the highest percentage of any city included in the study and above the national average, 9%.

Meanwhile, 2% of eighth-graders were excluded from the test, a lower number than several cities, such as Cleveland, where 11% were excluded.

Sample questions from the writing test can be viewed at nationsreportcard.gov. One question asked students to write a letter describing what a backpack is.

The education historian Diane Ravitch, who has served on the governing board of NAEP, said, “The conclusion we draw is we have some serious issues having to do with reading, writing, and math by the time kids are in eighth grade.”

The United Federation of Teachers president, Randi Weingarten, said the scores demonstrate that “school districts cannot test prep students into developing higher-order thinking skills.”

High school seniors were also tested, but their results were not broken down by city and state.