Faced with the prospect of 10,000 more students by 1997, the Howard County school board voted yesterday to try to increase its five-year spending for construction and renovation from $166.7 million to $210.9 million.

Added to the list of a dozen facilities planned or scheduled for renovation were two more elementary schools that would serve the state's fastest-growing school population.

Howard County's 50 schools now have about 30,000 students. Officials anticipate that about half the enrollment growth will be in elementary school students. The addition of two elementary schools to the long-range plan was prompted by anticipation of population increases in the northeastern and western parts of the county.

Yesterday's action called for $35.7 million in construction for the 1991-92 school year, when three new facilities are to open. They include Burleigh Manor Middle School, the replacement for Elkridge Elementary, and a school in the southeastern part of the county. About three-fourths of the fiscal year's capital construction would be financed through county bonds, school officials said.

The five-year plan includes $19 million in renovations and an addition at Wilde Lake High School, built 20 years ago as the county's first high school with movable interior walls. The school's capacity would be increased from 920 students to 1,200 and its electric cooling and heating system would be updated.

Also planned is a $5.3 million environmental science center for the entire school system. It is scheduled to be completed in the Middle Patuxent River Valley near Clarksville in 1993.

The board voted yesterday to move up by one year, to 1994, the opening of the county's ninth high school, planned for the western part of the county. It would be the first constructed since Centennial High opened in 1977. Board members expressed some worry that the new school might not be ready in time.

The budget proposal goes next to the state Interagency Committee for Public School Construction for review.

There is some concern about how the plans will be regarded by a state facing a $150 million deficit, said Rosemary Mortimer, president of the county PTA Council. "All these things are very expensive . . . . It is foolish to think it {the deficit} would not affect Howard County."

Based in part on what the state says it would contribute to school construction, the county school board plans to submit a final budget proposal to the county executive and County Council for approval next spring.

School officials indicated that the five-year improvement plan could be revised if growth is slowed by enactment of an ordinance requiring adequate public facilities, such as roads, to service new construction.