Washington -- long the 'Capital of Leaks'

Some people think you couldn't run Washington without news leaks. Washington is probably the most open capital in the world.

Has it gone too far? Some officials here have submitted themselves to lie detector tests in order to prove they were not the ones leaking material to the press.

President Reagan at this week's press conference said, ''I do think it reached a new high here, of the leaks that were destructive of the foreign policy we were trying to conduct, that endangered delicate negotiations. . . .'' Some officials say there is cause for genuine alarm; others take a ho-hum attitude and recall there had been concern about leaks (perhaps justified) long before President Kennedy told his press secretary, Pierre Salinger, to run down the source of a particular leak and got the report that the culprit was Kennedy himself.

The American system of separation of powers does much to make Washington the Capital of Leaks. Under a parliamentary system, the front bench government spokesmen confront the opposition and debate matters of public concern in detail. In Washington, the give and take of the presidential press conference sometimes fulfills the same purpose, but this varies by president: Franklin Roosevelt had 998 press conferences in 12 years; Ronald Reagan has held seven in a year. The FDR conferences were on radio, and the President was quoted in the third person. Mr. Reagan's voice and expression are immediately visible on television.

Meantime, the traditional progression of a presidential term has proceeded. Mr. Reagan has finished up his ''honeymoon'' period after his first year; now the novelty of his personality and way of handling Congress have moved into the next stage. This is apt to create a more competitive and often a more combative relationship with the press. The midterm election comes next and then 1984.

The relationship of the press and the president in Washington is symbiotic; both gain from the other. The president can and does use the media to present his program favorably; the media are eager to get the news and to question their favorite ''source'' about what it means. The relationship is so important that regular conferences and briefings are held every day and even obscure governmental agencies have press officers. Nobody can precisely differentiate a legitimate piece of supplementary information from a deliberate ''leak.''

Nearly every new Washington administration goes through a period of irritation or anger over leaks, though there is a tendency to accommodate itself to it after awhile. It learns that leaking is a two-way game, and it can become more adept at it.

In rare cases, the administration undertakes a general counterattack. In President Nixon's day, this went so far as a challenge to the legitimacy of the media itself, a campaign carried on by Vice-President Spiro T. Agnew. A 1979 study found hangovers from this attack, in the form of ''popular dissatisfaction with, and hostility toward, the news media,'' with portions of the public neither believing the administration nor the reporters writing about it.

President Reagan is handling the present situation gently. A recent Time magazine article notes that the Wall Street Journal disclosed a State Department memo discussing ways of putting pressure on the military regime in Poland. The article also referred to Washington Post reports on ''a secret Pentagon study indicating that military costs over the next five years may be $750 billion more than now projected.''

Mr. Reagan told his Jan. 19 press conference: ''I've been told repeatedly that what is happening is nothing new, that it's been done under other administrations.'' He insisted, however, that the situation has become serious and said he has assigned his new national security adviser, William Clark, to look into it. Disclosing classified government material is a crime, he noted.

A new guideline says: ''All contacts with any element of the news media in which classified National Security Council matters or classified intelligence information are discussed will require the advance approval of a senior official. In the event of unauthorized disclosure, . . . government employees who have had access to that information will be subject to investigation to include the use of all legal methods.''

Washington waits to see how the new investigation and the new relationship between government and media works out. Since Franklin Roosevelt's day, the press community here has been largely self-policed. The relationship is difficult because there are no precise rules. But generally the system works reasonably well.