The opening of Metro's Orange Line extension to Ballston yesterday means that 33.7 of the planned 101 miles of subway are in operation. It may be another decade before the entire system as presently planned is completed.

Here is the schedule for opening Metro lines after Ballston: Blue Line

The next Metro segment to open will be the Blue Line extension from Stadium-Armory east under Benning Road and East Capitol Street into Prince George's County at Central Avenue and Addison Road. That segment is scheduled to open late in 1980.

Early in 1982, if Metro is able to make up some construction time lost because of a concrete pier problem, the other end of the Blue Line from National Airport south through Alexandria to Huntington in Fairfax County will be opened for operation. Red Line

The Red Line is scheduled to be extended north from Dupont Circle under Connecticut Avenue to Van Ness Center and the University of the District of Columbia late in 1981. The rest of that line, which runs under Yuma Street to Tenley Circle, then north under Wisconsin Avenue and Rockville Pike all the way to Shady Grove Road in Montgomery County, will open late in 1983.

The other end of the Red Line, which now ends at Silver Spring, is scheduled for completion from Silver Spring north to Glenmont late in 1980. Orange Line

All of the Orange Line is now open except the Falls Church-Fairfax County extension west from Ballston. That segment, which will terminate at in the Vienna station at Nutley Road and Interstate 66 is scheduled for completion in mid-1985. Yellow Line

The Yellow Line shares track with sections of both the Blue and Green lines, but it has two segments that stand alone. One is the Potomac River crossing of Metro that will provide a nonstop connection between the Pentagon and L'Enfant Plaza stations. That connection, which extends north under 7th Street SW from L'Enfant Plaza through the Archives to the Gallery Place station on the Red Line, is scheduled to open late in 1982.

The other stand-alone section of the Yellow Line extends from King Street Station in Alexandria west to Van Dorn Street, then south into Fairfax County to the planned Franconia-Springfield station near Springfield Mall. The line from King Street to Van Dorn Street is scheduled to open late in 1984; the remaining leg to Franconia-Springfield is scheduled for the middle of 1985. Green Line

The Green Line shares track with the Yellow Line between L'Enfant Plaza on the south and Greenbelt on the north, in Prince George's County. It will be opened in several segments.

The first segment to open will be from L'Enfant Plaza through Southwest Washington and the Navy Yard and across the Anacostia River to the Anacostia station, near Howard Road and the Anacostia Freeway.That will be completed by the middle of 1985.

That southern leg will then be extended on a line generally parallel to Wheeler Road through St. Elizabeths Hospital and south into Prince George's County to the Rosecroft Raceway area. The scheduled completion date for that extension is late 1986.

The northern leg of the Green Line from L'Enfant Plaza north under 7th Street to U Street, west to 14th Street, north to the general area of 14th and Harvard Streets NW, then northeasterly across Georgia Avenue and into Fort Totten, where it will intersect the Red Line station there. The line will then continue into Prince George's County and north to Greenbelt.

The lengthy segment from Gallery Place north to Prince George's Plaza is scheduled to open in mid 1989. The remaining segment, between Prince George's Plaza and Greenbelt, is now scheduled for completion early in 1990.