Members of the Falls Church City Council angrily warned the Metro board yesterday that they are prepared to block continued financing of the entire regional subway system rather than risk having the planned West Falls Church station becoming the temporary end of the Orange Line.

Speaking for the council, Mayor Harold L. Miller demanded that Metro reshuffle funds so the subway can be built all the way to Vienna in one chunk before any passengers are allowed to ride on it.

Unless Metro agrees -- which its officials called doubtful -- Miller said the city manager would refuse to sign a regional agreement that would release $275 million in federal funds for continued construction on both sides of the Potomac River.

Joseph Alexander, Metro director from Fairfax County who headed the committee that negotiated the agreement, said it must be signed by all eight local governments that are Metro's financial partners. Unless it is delivered to the U.S. Department of Transportation before Sept. 30, the end of the fiscal year, Alexander said the $275 million would be lost to Metro forever.

The Falls Church council voted unanimously Aug. 27 to refuse its support unless Metro guarantees that the West Falls Church station does not become -- even temporarily -- the terminal of the Orange Line.

Miller said he feared the terminal would inundate the west end of the city with unwanted traffic from Fairfax County and pose a hazard to more than 600 students at the George Mason Junior-Senior High School.

The Orange Line, a branch of the existing Blue Line, will open later this year from Rosslyn to the Ballston station in Arlington.

Metro had planned to extend the line in one chunk 10 miles farther to the west, to the planned Vienna terminal. But when the pending financial agreement was reviewed by federal officials, they insisted on breaking it into two segments -- to West Falls Church, which would be completed by 1984, and then to Vienna, opening in 1985.

Miller urged yesterday that the money be reshuffled to restore the old plan.

Alexander and Cleatus E. Barnett, acting Metro board chairman, defended the current proposal, saying it would be impossible to take money away from Maryland or the District of Columbia to satisfy Falls Church.

"We've been over it, and we've spilled blood . . . we've done the best we could," Barnett said.

Barnett said the city's demand could run afoul of federal regulations, which now require that transit projects everywhere in the country be built in relatively short segments that can be put into operation as rapidly as possible.

Despite their doubts, Metro officials said they would consider the Falls Church demand, and would sound out federal officials on relaxing the regulation.

A preliminary check by Metro found federal officials voicing no serious objection to the proposal if the problems can be worked out locally, Irving G. McNayr, executive director of the Northern Virginia Transportation Commission, told a meeting of that organization last night.

Alexander, also a member of the Virginia Commission, stressed at last night's meeting that Fairfax County is as eager as Falls Church to complete the entire Vienna Line as soon as possible.

On another matter, Richard S. Page, Metro general manager, reported that the subway system carried 82,000 passengers last Saturday, about 12,000 more than normal for that day of the week, and about 50,000 on its first Sunday operation. While the latter figure was less than earlier estimates of 75,000 to 90,000, it was higher than Metro planners' forecast of 35,000.