After reading the article "Segregation Soars in Maryland Schools" {Metro, July 31} the only thing I can say, as a citizen of Prince George's County and (I hope) a public school parent, is: ''No wonder!''

The article noted Prince George's County's magnet school program and quoted county School Superintendent John Murphy as saying, ''Segregation can't be considered a Prince George's County problem any longer.''

It is a pity Mr. Murphy didn't see fit to point out the fact that the county has a stranglehold on white families designated for magnet schools, whether or not the magnet program is of benefit to them, or that the county can and does prevent these children from attending other county schools which better serve their needs.

My five-year-old daughter is designated to a magnet school with a program that does not serve her age group, kindergarten. I have, since April, been seeking child care in the neighborhood of her designated school, but have found none available that can accommodate a child who spends a half day in school. I have repeatedly informed the school board of the fact, and yet my requests to transfer her to another nearby (and also predominately black) school where I have suitable day-care arrangements have been repeatedly denied, solely because my daughter is white.

No wonder Maryland's schools are so segregated. My family's experience is that Prince George's County is preventing an intelligent and highly motivated white child from attending public school. LETITIA HALL THOMAS Oxon Hill