Loudoun Memorial Hospital last week moved a step closer toward gaining approval of a $2 million expansion when the board of directors of the Northern Virginia Health Systems Agency approved the hospital's proposal for 27 additional beds.

A state health planning board will make its recommendation next week, and a final decision from the state health commissioner is expected by Christmas.

The expansion, which would give Loudoun Memorial a total of 146 beds, has general support in Leesburg but is opposed by residents from the Sterling-Herndon-Reston area, who want their own hospital. Last spring, the state health commissioner rejected a local group's proposal to build a 200-bed hospital in Reston, in part because of the availablity of hospital beds in Leesburg.

"We approved the Loudoun proposal because the hospital has a 90 percent use rate and because the people of Loudoun County are so far away from other hospitals," said Dean Montgomery, executive director of the Health Systems Agency. "I'm fairly confident the state commissioner will ultimately approve the project." Manassas Council Unwilling -To Finance New High School

The Manassas school board last week testified to the City Council in defense of its request for $11.5 million to build a new high school, but the council appeared unwilling to seriously consider granting the money.

"This proposal would mean a tremendous increase in taxes," said City Manager Roger Moore, who has estimated a 30 percent tax hike by 1986 would be needed to offset the costs. "There have got to be some less expensive alternatives."

School board Chairman Joseph Johnson said his group made the request to ease future space problems at the 29-year-old Osbourn Senior High School, which currently has 1,000 students.

The council has agreed to meet again with the school board to consider alternatives to the proposed new school.