Transportation Secretary Brock Adams told about 200 Washington area officials tonight that they must find a permanent and certain source of money to build and operate the Metro subway before the Carter administraation can guarantee annual appropriations for construction.

That funding source, which Metro officials are hoping will develop in the form of regional taxes dedicated to Metro from each of the three major Washington area jurisdictions, is the next logical step in assuring completion of the 100-mile Metro system, Adams said in a dinner speech.

At the same time, Adams said, the federal government will budget $275 million annually for Metro construction until Metro has exhausted about $1 billion in funds that can be transferred from canceled interstate highways.

That would leave Metro about $1.1 billion short of the federal aid needed to complete the system that all area jurisdictions have said in recent votes they want to complete.

Adams' speech came amid a two-day conference here at which the Metro board hopes to build a regional concensus on the best way to assure longrange financial security for construction of the subway and operation of the combined bus and subway system.

Metro now leads a hand-to-mouth existance financed through the good will of seven loval governments. The Metro operating deficit is about $100 million for bus and subway this year and has been projected to climb as high as $500 million in inflated dollars by 1990, depending on fare levels and ridership.

Any one of Metro's partners can simply withhold funds' as Fairfax City already has done. If a major partner such as Montgomery County or Fairfax County stopped paying, Metro would stop running.

"I don't want Metro to be like the Community Chest," Adams said. "But without that local commitment to run the system, I cannot promise you a place at the head of the line, or even in the line" for federal grants after interstate highway money runs out.

Almost all big city transit systems have a guaranteed tax source to pay for operations. Adams said such cities would receive priority for federal transit construction grants.

Adams' $275 million funding level for the next two years is about $125 million short of what Metro hopes to receive under a proposed financial plan calling for completion of construction in 1987.

If that smaller level were to continue for the next few years, according to Metro documents, Metro could not be completed before 1989 at the earliest and the total construction cost would be "several hundred million dollars" higher than the current best estimate of $6.8 billion.

Neal Potter, new president fo the Montgomery County Council, told Adams that the lower level was understandable during the administration's attempts to control inflation but expressed hope that it could be increased in the future. Adams supported the inflation fight but was noncommittal on a future federal increase.

The meeting here involves members of city and county councils and boards, state legislators from Maryland and Virginia, congressional staffers and others with an interest in Metro.

District of Columbia, Maryland and Virginia participants caucused last night and adopted resolutions supporting some kind of regional tax dedicated to Metro.