August 21, 1981

For six years the battle had been joined, in court and out. The Crow Indians on the reservation near here argued that a 52-mile stretch of the Bighorn River that crosses their land belonged to them, and they closed it to non-Indian fishermen. The State of Montana argued that the banks oust after 4 A.M. with about 15 cars, pickup trucks and campers parked athwart both lanes. A sign at the front of the bridge read: ''Crow Reservation Closed to Fishing Today, Tomorrow and Forever.''

A two-day printers' strike that effectively silenced most of Poland's major newspapers, ended today on an angry note. Solidarity, the independent trade union, threatened an even wider shutdown that might include television and radio. Aroused by government inquiries into the legality of the strike and by one reported threat to use force to dislodge union militants at a Warsaw printing plant yesterday, the printers said they were maintaining a nationwide strike alert and had only suspended, not halted, their action. Lech Walesa, the national union leader, had to visit strikers occupying a large printing plant here to persuade them to return to work. At a meeting at the union's Warsaw headquarters, he predicted that another confrontation over the union's demand for regular access to the official media was ''inevitable.''

The Federal Reserve Board moved to provide emergency credit for financial institutions at rates as low as 14 percent. The action, welcomed by the troubled thrift industry, is meant to offer longer-term credits than the two- to three-day loans now available. (Page D1.) American families' real income fell 5.5 percent last year, the biggest decline in the 34 years the Government has been keeping track, the Census Bureau reported. This raised those formally classified as poor to 13 percent of the population, from 11.7 percent in 1979. (A10.)

IT is getting chilly on the Hampton beaches early in the morning; it is cool in the Berkshires late at night. The summer is waning, although some of its entertainments are still intact. One of them is summer theater, which this season is rich, as always, in comedies, musicals and classics, and short, as always, in straight plays, especially somber ones. Somberness in summer theaters is sanctioned only in classics, preferably Elizabethan. The names in summer theater this year are Hart, Gershwin and Shakespeare, not O'Neill, Williams and Miller, although many of the summer productions are uncommonly ambitious. Once, the strawhat circuit was just a poor cousin of Broadway; now it is more like an adjunct. Consider, for example, Moss Hart's ''Light Up the Sky,'' which is at the John Drew Theater-Guild Hall in East Hampton, L.I. It is the quintessential summer comedy. It had a moderate success on Broadway, running for 214 performances after it opened in 1948, but somewhere or other, it finds a home every summer. ''Light Up the Sky'' is a comedy about Broadway, and the production at the John Drew features Broadway actors: Danny Aiello (in the role Sam Levene did in 1948), Gloria Grahame, Phyllis Newman, Michael Lipton, Sylvia Sidney and Russell Nype.

Reagan Administration officials said today that their decision to hold naval exercises in waters claimed by Libya was intended to affirm the right of free passage in international waters and not continue to allow even the appearance of letting Col. Muammar el-Qaddafi set the rules. The possibility of an air clash, such as the one that occurred yesterday with the reported downing of two Libyan fighters, was not regarded as inevitable, nor was it considered out of the question, several officials said. But they said that because President Carter refused to allow American planes to fly over the Gulf of Sidra during similar exercises last year, there was considerable pressure from the Navy not to allow a precedent to be set. In 1973 Colonel Qaddafi, the Libyan leader, established a line across the mouth of the Gulf of Sidra as a ''base line,'' south of which Libya claimed as its internal waters. The American officials said that almost yearly since then, American planes and warships had crossed that line. But last year, because of the crisis over the American hostages in Iran, and because of a desire not to cause unnecessary agitation in the region, Mr. Carter did not permit American air or naval craft to go farther south than three miles north of the line.