U.S. District Judge Thomas C. Platt ruled yesterday that the Professional Air Traffic Controllers Organization (PATCO) was in contempt of court and must pay a $100,000 penalty for an air traffic slowdown in May and June.

Furthermore, it was learned yesterday, the Federal Aviation Administration (FAA) will be meeting this week with Justice Department officials to determine if possible criminal sanctions against controllers could result from the slowdown.

If Judge Platt's ruling in the federal court in Brooklyn withstands appeal, it will be the first time the powerful controllers' union has been fined. A spokesman said PATCO will appeal the ruling, but declined further comment.

The finding of contempt arose from a slowdown at Washington National and other airports May 25 and 26 and June 6 and 7. Controllers began slowing down air traffic after PATCO warned such an action was possible if airlines did not permit controllers to make free, unconditional "familiarization" flights to Europe and the Far East.

In his decision, Judge Platt found that the controllers had violated a 1970 injunction against slowdowns, sick-outs, strikes and similar actions. The motion seeking enforcement of the injunction was brought against PATCO by the Air Transport Association of America (ATA), which represents most of the major airlines.

In a footnote to his decision, Judge Platt said that "it is also the sworn duty of the attorney general to enforce these laws, but for reasons not fathomable to this court, they have yet to initiate any investigative or enforcement proceedings."

Controllers are FAA employes. The FAA has traditionally been reluctant to confirm that a slowdown is in progress even when the fact is obvious to anyone at an airport. In the case of the June 6 and 7 slowdowns at Washington National, however, tower chief Harry Hubbard broke from that position and told reporters, "It is a slowdown, and you can quote me."

Senior FAA officials said yesterday that a large quantity of materials - including air traffic control tape recordings - had been studied and would be central to the discussion with Justice Department officials.

PATCO actually stipulated in court papers that it had entered into a slowdown. However, PATCO insisted that the 1970 injunction was no longer in force because of a legal precedent in another case. By finding the injunction to be valid, Judge Platt also accepted the stipulation that a slowdown had occurred and that $25,000 had to be paid by PATCO to ATA for each of the days of the slowdown.

Judge Platt also delivered a lecture to PATCO on the slowdown tactics. In his opinion, Platt wrote, "In addition to the essential public services which the defendants provide, they are, I am sure, mindful of the fact that they have the lives of many thousands of people in their hands to neach and every one of their working days. The court does not even wish to entertain the notion at this time that one would willfully trifle with such awesome responsibility in such a way as might possibly jeopardize the lives of one or more members of the innocent traveling public."

Pilots and airline representatives complained during the slowdown that unsafe conditions were resulting from planes being stacked in approach patterns while awaiting landing instructions and while flying unusual roundabout routes from airport to airport. ATA also cited extra fuel consumption as a major cost caused by the slowdown.

In addition to Washington National, other airports reporting major slowdown problems included Pittsburgh, San Francisco International and New York's LaGuardia.

Judge Platt suggested that if the controllers did not like the working arrangements they were able to negoatiate, their solution "is to seek other employment, not to engage or encourage conduct which violates the law at the expense and possible endangerment to the lives of innocent people . . ."