Despite some recent improvements, a large majority of schoolchildren are unable to write clearly and proficiently, according to a federally funded report that calls student writing skills "depressing."

The problem cuts across race, age and gender, and has persisted for a decade in spite of increased classroom attention to writing, the report said. The improvements in recent years only restored skills to their 1974 level.

Poor writing skills are generally thought to reflect inability to think and communicate clearly. The new findings follow other recent indications that writing skills have declined, as some universities report increased enrollment in remedial writing classes and some businesses establish writing workshops for new employes.

The report, prepared by the National Assessment of Educational Progress, covered 1974 to 1984. It measured writing performance in three age groups -- 17, 13 and 9 -- and their ability to handle three basic writing tasks: a "persuasive" letter, a factual description and an imaginative, creative essay.

Eighty percent of the 17-year-olds and 90 percent of the 13-year-olds were unable to write an adequate persuasive letter, the report found. The 9-year-olds were given an easier task, but 66 percent performed it inadequately.

They were asked to write their fictitious "Aunt May" and try to persuade her to let them travel alone to visit her. In a letter typical of those judged totally inadequate, one youngster wrote:

"I know everybody say I to little to travel but I'm not if you give sometimes give kids a chance to prove prove something to you maybe it won't be so bad. Maybe we can help you to give kids a chance." That letter was signed "your nice" instead of "Your niece."

The children did slightly better on the other writing tasks, but majorities still performed inadequately. More than 75 percent of the oldest were unable to write an imaginative, creative essay, as were more than 80 percent of the 13-year-olds and almost all the 9-year-olds.

Results were similarly bleak for the writing of a simple factual description, with no opinion and no creative thinking involved. Sixty-two percent of the 17-year-olds, 81 percent of the 13-year-olds and 97 percent of the youngest children were unable to do so.

Researchers called the results "disappointing," since they came after a stepped-up effort by schools to give children more instruction in writing. The survey found students in all age groups receiving more writing instruction, although most said they still do about the same amount of writing on their own.

The average number of school papers written by 17-year-olds was the same in 1984 as it was a decade earlier -- less than one essay or report a week, counting all subjects.

"Teachers are doing more, and they are trying harder," said Ina V.S. Mullis, associate director of the National Assessment of Educational Progress. "There just needs to be further research" into effective ways to teach good writing, she said. She also suggested that better teacher training might help.

The one bright note in the survey was a finding that writing performance improved in the last four years of the report, after declining in the late '70s. "If one wants to look for some good news, the trend lines are moving in the up direction," said Archie Lapointe, director of the assessment group.