IS GEN. MANUEL Antonio Noriega losing his grip? The Panamanian strong man, unable to intimidate his restive, democracy-seeking countrymen, has put on a new display of muscle. He sent out an armed party, guns blazing, to seize Col. Roberto Diaz Herrerra in his home; this is the maverick officer, his erstwhile No. 2, whose allegations of crime and corruption against Gen. Noriega precipitated the crisis the country is now passing through. Gen. Noriega also occupied La Prensa and other independent publications. By these acts the general evidently means to isolate the population from sources of opposition to him. He is acting like his friend President Daniel Ortega of Nicaragua, who, seeing an opening for a little exercise in anti-American expediency, paid a sympathy call.

For years it was the accepted wisdom that Panama was a place where the people preferred stability and political theater to the rewards and rigors of democratic government. The revelations of Col. Diaz, however, seem to have uncorked a heretofore untapped well of democratic sentiment. Mass protests have gone on in the streets for weeks. An immensely successful general strike has just been concluded. Important elements in the banking and business communities, often thought of as bulwarks of the old system of military rule with a political facade, appear to be concluding that maintenance of Gen. Noriega is a guarantee of endless turbulence. Currency is said to be flowing out of the country; since Panama's currency is the American dollar, there can be no possibility of printing up more.

A military leader with a strong sense of duty would be considering retirement. Gen. Noriega, however, appears to lack a strong sense of duty. Meanwhile, the Panamanian people are showing a readiness to keep the pressure on. Fortunately, the American government, having long cultivated the military in order to serve a strategic interest in the Panama Canal, is now unequivocally identified with the forces of democracy. So much is this now the case that Gen. Noriega is able to evoke a specter of American ''intervention'' in order to rally nationalist sentiment for his own personal benefit. In fact, what is happening is that Washington is stepping back and exposing him to the anger and impatience of his own people.