Eleven private school students and 27 enrolled in public schools in the Maryland and Virginia suburbs were named semi-finalists this year in a national scholarship contest for blacks.

St. Alban's School, a private school for boys affiliated with Washington's Episcopal Cathedral has more top-scoring students this year in the contest for than any other high school in the Washington area.

The five semi-finalists at St. Alban's - half the blacks in its senior class - are among 27 students at private schools in Washington who received top scores in the annual National Achievement Scholarship Program for Outstanding Negro Students.

By contrast, the District's public schools, which enroll about 10 times more black students, had only 14 semi-finalists in the contest.

Among Washington's public schools, those with the most semi-finalists - four each - were McKinley High in Northeast and Wilson in upper Northwest. Springbrook High School in Silver Spring (Montgomery Couny) had three semi-finalists.

Two private schools also had three semi-finalists apiece - Sidwell Friends in Northwest Washington and Takoma Academy in Takoma Park, Md.

The relatively large number of blacks in private schools who socre high on the national tests - even though relatively few blacks are enrolled in them - is part of a pattern in the test results for the past several years.

The semi-finalist were picked on the basis of a 100-minute multiple choice examination in English and mathematics, sponsored by the National Merit Scholarship Corporation.

About 60,000 black students throughout the country took the test last fall. They were among about 1 million high school juniors taking the exam, which is similar to the Scholastic Aptitude Test (SAT) of the College Entrance Examination Board.

Last month about 15,000 students with the highest scores - regardless of race - were named as Merit Scholarship semi-finalists.This week the highest-scoring black students, about 1,500 nationwide, were named as National Achievement semi-finalists.

According to the published lists of winners, six black students in the Washington area scoed high enough to qualify as Merit semi-finalists as well as semi-finalists in the achievement program. Last year only one black student did so.

Five of the black Merit semi-finalists attend private schools in Washington and the sixth is a student at W.T. Woodson High, a public school in Fairfax County.

Next spring about 575 students throughout the country will be chosen for National Achievement scholarships. Most of them are given by companies and universities.

Among the semi-finalists in Maryland, 13 attend public schools in Montgomery County, and seven are in Prince George's public schools. In Virginia the Fairfax County schools had six semi-finalists, Arlington and Alexandria, none.

Last year Washington's public high schools had about 25,000 black students, compared to about 2,200 in private schools.

At McKinley High the four semi-finalists came from a class of about 800 black students and only three non-blacks - one white, one Hispanic, and one Asian. At Wilson, the four semi-finalists are in a class of about 400 blacks, and 300 whites, Hispanics, and Asians.

At. Alban's, which is selective and expensive about $3,000 a year, although it has some scholarship students, the 10 blacks are part of a senior class of 71.

According to a survey of both white and private schools, many of the National Achievement semi-finalists have college-educated parents - most often teachers and middle-level civil servants, but also several lawyers and dentists. School officials said some of the semi-finalists have parents with non-professional jobs - including at least one barber and one janitor - but the preponderance of them seem to have middle-class backgrounds. At the private schools, officials said, only a few of the semi-finalists are receiving financial aid.

Here is a listing of Maryland students who have qualifed as Achievement Program Semi-finalists. The final awards will be announced March 22, 1978.

Yasmin A. Walters, Bethesda Chevy Chase High School: Rosalyn E. Jones Stone Ridge C.D.S. Saered Heart; Christopher A. Swaby, Walter Johnson High School; Tonva V. Parham, Elizabeth Seton High School: Hilton C. Ray. Bowie Sr. High School: Cathleen R. Drew. Oakland Mills High School: Karen M. Ferguson. Oakland Mills High School: Cherie M. Caldwell. Wilde Lake High School: Rosalyn A. Jackson and Michael D. Julius. Eleanor Roosevelt Senior High School: Tracy C. Arnold and Tonda V. Taylor. Regina High School: Terri R. Grant. Albert Einstein Senior High School: Nanc I. Ruiz and Sabrina C. Williams.Duval Senior High School: Vidal E. Hayes. Potomac High School: Karen J. Holloway. Winston Churchill High School: Darrel E. Dent. Parkdale Senior High School: Carla A. Thomas. Colonel Z. Magruder High School: Charles D. Batchlor and Cheryl L. Parks. Robert E. Peary High School: Cynthia Woods. Montgomery Blair High School: Keith H. Morton. Northwood High School: Carolyn R. Fletcher, Marc D. Lawrence and Lisa R. Mundy. Springbrook Senior High School: Terry E. Haugabrook. Suitland Senior High School: Jonathan Armstead, John D. Butler, and Michelle C. Cochrane, Takoma Academy.