Transportation Secretary Neil Goldschmidt and Metro General Manager Richard S. Page yesterday formally signed an agreement that Metro and the federal government, will share a $1 billion Metro construction debt.

Although that painstakingly negotiated agreement removes a major obstacle in federal-Metro relationships, Goldschmidt lost no time in reminding Page and Metro board members who attended the ceremonies that much work remains to be done.

Metro, Goldschmidt said, "lacks only one key component for certain success -- and that is an adequate, assured source of funding from the jurisdictions served by the Metro system. That funding source must be nailed down."

Both the Maryland and Virginia legislatures are expected to consider in their next sessions proposals from the Washington area for special taxes earmarked for Metro construction and operating costs. Today, those costs are paid primarily by local governments out of their operating budgets, which means that the politically sensitive real estate property tax is keeping Metro going.

Under the terms of the agreement, Metro has until Aug. 15, 1982, to have "stable and reliable" sources of funding in place. If such sources are not identified, then the federal government has no further obligation to provide construction funds to Metro.

Goldschmidt implied that the administration has not figured out exactly what to do about the Stark-Harris bill, House-passed legislation that authorizes full funding for completion of Metro's planned 101-mile system. The White House opposed that bill the day it came to the House floor.

Goldschmidt said, he is hopeful that "before that matter runs its course we will be on the side of the good guys."

In the long run, he said, Metro "can't survive apart" from national transit programs, as it has done at least partly in the past. On the other hand, Goldschmidt acknowledged that there was "real history" behind special legislation for Metro.

Goldschmidt said that as the District of Columbia becomes more and more a full partner in United States affairs, "it makes it harder and harder over time to create special categories" of federal assistance for the Washington area.

"The attitude I have found in the White House [concerning Metro]," Goldschmidt said, "has been quite good."