The regional task force that is studying alternatives to the planned 100-mile Metro subway system reduced yesterday from 1,764 to 72 the number of options it will continue to consider for a revised Metro system.

The mind-boggling chore, accomplished by area politicians and planners after months of study and a $625,000 consultants report, sets up the possibility of a dramatically revised Metro network beyond the 60 miles now fully scheduled and financed.

Among the options now clearly on the table are:

The elimination of the Yellow Line from Alexandria's King Street Station west to Springfield.

The rerouting of the Orange Line through Arlington and Fairfax counties so that its western terminal would be a tTysons Corner, instead of Nutley Road and Interstate 66 in Vienna.

A termination of the northern leg of the inner-city Green Line at Columbia Heights, near 14th and Kenyon Streets NW. That would mean the elimination of the Kansas Avenue NW and Prince George's County sections of that line.

A rerouting of the southern leg of the Green Line from a terminal now scheduled inside the Beltway near Branch Avenue in Prince George's to a new terminal outside the Beltway near Rosecroft Raceway.

The consultants to the regional task force, Peat, Marwick, Mitchell & Co., will now study each of the possible 72 combinations for ridership potential, construction costs and operating expenses.

Then the politicians will have to reduce the alternatives once more - first to three system options, then to one, agreed-upon regional system. The entire process is scheduled for completion sometimes early next year.

The entire exercise is part of the federally ordered "alternatives analysis" that the region has undertaken to decide if the 100-mile system as presently planned can still be justified in terms of cost.

The 100-mile system was laid out in 1969. Are the lines still in the right places? Would a bus network or trolley system work as well?

With the area transit system redefined, local politicians can construct a financial plan for building and operating that system. Transportation Secretary Brock Adams said this week he wants that plan immediately, and in any case must have it before he will approve federal financing for any more of the subway.

Adams also said that the planned subway lines would have to compete with each other for federal financing because there is not enough federal money to go around.

Adams' remarks were made with reference to the proposed extension of the Red Line from Silver Spring to Glenmont in Montgomery County. That extension is not a part of the regional task force study, but the financing of the Glenmont line will have to be considered along with the rest.

Area officials, including Montgomery County Executive James P. Gleason and Metro general manager Theodore Lutz, see the Adams statement as potentially highly divisive, in that it pits one jurisdiction against the other for construction money.

But Arlington County Board Chairman Joseph Wholey said yesterday after the regional task force meeting that he thinks major blood-letting can be avoided. Wholey said the figures in an Adams letter to Metro indicated "the likely availability of about $5 billion for Metro construction. I think that what we finally recommend is going to be within that figure."

According to figures provided by Lutz, the 60-mile system already funded will cost $3.3 billion. Another $400 million to $500 million has been spent on construction of short segments of the Green and Yellow Lines in the mid-city area.

Adams, in his letter, said a total federal funding capability of $1.2 billion remains for Metro. However, he said, the present system will cost about $1.8 billion.

Lutz yesterday called that figure probably too hgih because it includes all contingencies. Furthermore, Lutz said, Adams' figures do not include the availability of any local money.

"I do not like the tenor of this letter in that it suggests that local officials have to shift from a regional approach to one of deciding how to cut their losses," Lutz said in an interview. He said he, too, thinks a total system can be built for around $5 billion.

Adams said in a press conference that the two-year-old federal ceiling of $4.7 billion still applied to Metro, but his letter did not contain that ceiling.

With that as background, the regional task force yesterday approved for further study by the consultant the following options in each of four corridors:

Green Line, Northern Leg

Four options are still under study, with a fifth to receive special consideration. They are (1) to leave the presently planned line in place; (2) to realign the route so it will terminate at the junction of Interstate Rte. 95 and the Capital Beltway; (3) to cut the line at the Columbia Heights Station in Washington, and (4) to do nothing to improve transit service. Also to receive study is a plan to improve the existing commuter rail service provided in the corridor by the Chessie System.

This leg is probably the most potentially controversial in the region because it pits the Prince George's County Council against the state of Maryland. Maryland wants the line moved to the I-95 junction.

That alignment would bring trains close to the College Park Woods subdivision, a politically well organized area that is opposed to the potential neighborhood disruption. The Prince George's County Council has opposed the I-95 option and its representatives voted against it yesterday at the task force meeting.

The consultant study shows that the I-95 junction proposal would generate the most riders for the Metro, but would have a slightly higher operating deficit than the present route.

Green Line, Southern Leg

Only two options are still under study, and neither of them retains the present planned alignment of the Metro, which generally follows Suitland Parkway and Branch Avenue. Under the first option, the line would bend south in Washington and cut through St. Elizabeths Hospital, then parallel Wheeler Road to Rosecroft Raceway.

Under the second option, the line would go through St. Elizabeths, then return generally to the Suitland Parkway-Branch Avenue alignment. Both proposals showed high ridership potential in the consultants study and proved cheaper than improved bus service feeding a closer-in station.

Yellow Lines

The portion of the line under study extends from Alexandria's King Street station west along the Beltway, then south into the Springfield/Franconia region. Three options were adopted yesterday. They are (1) to eliminate that segment completely on the grounds that the Shirley Highway bus lanes can provide the transit service needed; (2) to terminate the ine at the Van Dorn Station, and (3) to run the line to Franconia but eliminate the generally inaccessible Springfield station.

Additionally, a special study would be done on integrating proposed commuter rail lines from Manassas and Woodbridge with Metro service at King Street.

Orange Line

This line is planned to extend from the ballston station, now under construction, west to Vienna in the Interstate Rte. 66 median. Three options were adopted. They are (1) to leave the line where it is, but increase the parking at outlying stations in Falls Church and Fairfax County; (2) to change the route so that it runs along the Dulles Access Road to Tysons Corner instead of in the middle of Interstate 66, and (3) to terminate the route at the West Falls Church station.

That last alternative is opposed by the Falls Church City Council which is concerned about the impact of traffic at the end of the line. It was included as an option "so we can set it to rest," Fairfax County Supervisor John Shacochis said.

Peat, Marwick, Mitchell & Co. will now develop projections on construction costs, operating costs, patronage, revenue and the amount of subsidy needed for each of the options.