Although it had been threatened earlier this month, the Polish crackdown - when it came Tuesday night - on cultural exchanges with the United States and on both official and unofficial visas for Americans still took the American Embassy here by surprise.
It got the news during the evening - following its issue through the official Polish news agency - from a Western reporter.
It had had no previous hint that the Poles were, in fact, about to follow up on Gen. Wojciech Jaruzelski's angry criticisms Dec. 3 of Washington policy on Poland and his threat to limit cooperation in various spheres and retaliate over what he called ''unprecedented'' US visa restrictions.
A reading of the text of the Polish statement suggests that in one area at least - the total exclusion of Polish visas for personnel of the US Information Agency - the effects could be more far-reaching than might seem at first sight. The text refers to suspension of granting visas to all representatives and employees ''whatever'' of the agency or of what were called ''its branches.''
One of the most prestigious and valuable that may be affected is the Fulbright scholarship program, an official US government exchange program, which at present has sent about 20 Polish academics and students to American scholastic institutions and brought a similar number of Americans here for study and research.
The President's proclamation of a ''day of prayer for Poland and solidarity with the Polish people'' for last Sunday seems to have touched off the final decision.
''The 'day of prayer,' '' an official Polish source said, ''was organized without waiting to see what the general (Jaruzelski) might say Sunday evening (in his TV broadcast) or for the parliamentary session begun the next day to start the suspension of martial law. No notice is taken of the release of the internees. That's a deed - not words.''