Oct. 21, 1962 - There is an unmistakable air of crisis in the nation’s capital tonight. President Kennedy and the highest Administration officials have been in almost constant conference all weekend. Mr. Kennedy is expected to give the country an explanation in a radio-television address in the next day or so, but he has wrapped a tight veil of secrecy around the source of his concern thus far. Meanwhile, the Navy and Marine Corps are staging a powerful show of force in the Caribbean not far from Cuba, which has been the site of a large Communist military buildup in recent weeks. About 40 ships are heading for the island of Vieques off Puerto Rico. The Administration denies that there is any connection between the anxious mood in Washington and these maneuvers, which involve about 20,000 men, including 6,000 marines. But the speculation in Washington was that there had been a new development on Cuba that could not be disclosed at this point. By this afternoon, some decisions appeared to have been reached, and Administration sources indicated that the country would be informed shortly.