Glancing quickly at the two statements prepared for him on the Professional Air Traffic Controllers Organization's strike, President Reagan reached for a white pad to write his own version and suddenly said: Let me see the nostrike oath; I want to use it.

The time was Monday morning, the day the strike started. The place was the Cabinet room. Transportation Secretary Drew Lewis, author of one of the two prepared statements (the other was the White House staffs), quickly produced the no-strike pledge taken by all controllers. Reagan wrote his statement, including the entire no-strike oath.

Then, minutes later, he stepped into the Rose Garden to go on TV and teach the striking PATCO union a lesson they were learning the hard way. It was the same lesson that House Speaker Thomas P. (Tip) O'Neill and other now-wiser Democratic grandees recently learned -- also the hard way.

The lesson: when Ronald Reagan picks a target, he is as blunt and stubborn as a sledge hammer, despite his velvet glove of affability.

Among the 13,000 striking controllers, learning that lesson will cause anguish, tears and probably tragedy after the excitement of early combat wears off. For behind the cold. anti-strike logic pouring from Lewis' Transportation Department, Attorney General William French Smith's Justic Department and the editorial pages of The Washington Post and The New York Times, Reagan's sense of his own rectitude is the real guarantee against retreat.

That extends the president's sway beyond the Democratic-controlled House, where Tip O'Neill and his aides learned to their surprise that an ideologically committed conserrvative president could bend the House to his will on radical budget and tax reform. It puts on display a president willing to assume his righteous pose of union-busting strike-breaker without apology.

"Don't forget that Cal Coolidge is one of this president's favorite characters," a top Reagan adviser told us. Gov. Coolidge of Massachusetts broke the Boston police strike in 1919, the key event in his becoming president three years later.

Weeks before PATCO President Robert E. Poli pulled his men out on strike, back in June during the first potential crisis, Reagan had counseled Lewis against offering more than the $40 million settlement package then on the table. Reagan stayed near the centger of the long negotiations between the government and the union. He privately labeled the strike threat a virtual declaration of war against the government and he feared that any settlement over the $40 million mark would undermine his anti-inflation fight and crack his federal wage ceiling.

But the president's sense of timing made him acutely aware of the political advantages of taking a hard line in a labor crisis that might have been made in heaven for the glory of any president. The raise that Poli is demanding would give some of his members a higher salary and shorter working hours than the secretaries of state and defense (and all other Cabinet members). That would not make emotional allies out of blue-collar workers.

Along with the no-strike oath, regarded by Reagan in the old-fashioned way as a solemn undertaking, the conditions that undrelay the union's strike were a political safety net for presidential intervention. The one threat was that, with 13,000 controllers on strike, the nation's airways might indeed be forced to shut down. That would lead to an irresistible public demand for ending the strike, playing into the union's hands.

The administration is meeting that threat frontally, decrying the scare tactics of Poli that passengers are risking their lives in daring to fly during the strike. Thus, five days into the strike, whatever course it takes and however militant the union remains, Reagan seems headed for political gains in the handling of his first labor crisis.

That gives him an early-term dimension denied recent predecessors: a third conspicuous presidential success in a row, this one far beyond the congressional budget and tax wars. Reagan is showing an ability to pick his targets well and to use the sum of his powers to gain his end, a performance likely to reverse the dangerous erosion of presidential power at a time the Western World has maximum need for a strong presidency.