Britain ruling the waves - and the air?

With the torpedoing of the Argentine cruiser General Belgrano, the British fleet in the South Atlantic has taken one more step in its strategy of escalating the pressure on Argentina.

The incident May 2 also must remove any lingering doubts in Buenos Aires about the effectiveness of British naval might in the conflict over the Falkland Islands, which Argentina seized April 2.

Doubts about British air power are likewise fading. The sinking of an Argentine patrol vessel and the damaging of another by Harrier jump jets--after the attack on the General Belgrano--suggest how effective British air power is.

It now seems clear that Britain has, more or less, effectively taken control of South Atlantic waters and is in the process of assuming control of the air as well.

Details of the various sea and air actions, however, are sketchy. Both sides continue to issue conflicting claims.

Truth, in a way, is a big loser.

But now Argentina is less boastful about its claims of victory over British forces. It admits the attack on the General Belgrano and loss of two Israeli-built Dagger jets.

The cruiser apparently suffered heavy damage in the attack by a British submarine off Tierra del Fuego. The ship, which had recently assumed the role of flagship of the Argentine Navy, is reportedly limping toward Ushuaia, an Argentine naval port at the tip of South America.

Whether the General Belgrano, the Argentine Navy's only cruiser, is out of action permanently is unclear. But it will have to undergo extensive repairs and certainly will not be available at an early date.

Meanwhile, speculation continues here that elements of the British Royal Marines and other elite British commando troops are already on the Falklands--probably the West Falklands, the less inhabited and less defended of the two islands.

Maj. Gen. Jeremy Moore, chief of Britain's commando forces, visited the British armada late last week to confer with Brig. Julian Thompson, commander of the 3,000 assault troops and Commodore Michael Clapp, the Navy chief of amphibious warfare.

Argentine military analysts suggest the Moore visit was a preliminary step to the British landing.

''All is in readiness on the island,'' said one analyst, ''to meet the British man for man.''

Gen. Mario Benjamin Menendez, Argentina's military governor of the islands, telephoned Buenos Aires late May 2 to say ''all is well and without problems. Long live the fatherland!''

But there are concerns about whether the 10,000-or-so Argentine troops on the Falklands will be able to resist a determined British attack. Many, if not most, of the soldiers are conscripts serving a one-year military obligation. They come largely from warmer regions of Argentina and are basically unprepared for the cold, inhospitable climate of the Falklands, particularly with the approach of winter.