August 6, 1982

Energy Secretary James B. Edwards witnessed a nuclear bomb explosion for the first time this morning and said he found it ''exciting.'' The nuclear test today was the first in two years to be opened to viewing by reporters. In response to a question, Mr. Edwards denied that his visit here was timed to coincide for publicity reasons with the anniversary of the Aug. 6, 1945, bombing of Hiroshima and with the debate today in Congress on nuclear issues. Asked if more tests are planned, Secretary Edwards responded, ''That's a reasonable assumption,'' adding, ''Some of our weapons now are more than 20 years old.''

Two dozen Republicans, including six Congressmen, defied the President and pledged to defeat a $98.5 billion tax bill. Page D1. WASHINGTON, Aug. 5 - The Senate today approved spending cuts totaling $12.6 billion over the next three years, completing its major work in the long process of reconciling previous budget proposals. At the same time, however, the Senate instructed its negotiators working with House members on a separate tax bill to aim at extending unemployment benefits by 10 to 13 weeks. Senate aides put the cost of extending the current maximum of 39 weeks at $1.3 billion to $1.9 billion but suggested that the price could be met by lowering the threshold at which those who receive benefits pay taxes.

PIANISTS and violinists have their paths laid out for them, but singers are often torn between two worlds. Take, for example, Benita Valente and Florence Quivar, who will be appearing tonight and tomorrow night in liturgical music by Beethoven and Mozart at the Mostly Mozart Festival in Avery Fisher Hall. Both won their early recognition in the concert and recital world. Success in opera has come late for both. Over the years, Miss Valente's soprano has been admired by connoisseurs and critics alike - her lieder singing praised for its ''perfect legato control,'' her oratorio work for its ''pure tones and birdlike trills.'' Miss Quivar's career as a mezzo-soprano is marked by high musicianship and versatility, her range of styles stretching from Handel's ''Messiah'' and the Verdi Requiem to Stravinsky's ''Oedipus Rex.''

Conservative Republicans, who have been increasingly concerned about the direction of President Reagan's economic policies, revolted today over proposed tax increases. A group of two dozen conservatives, including six members of Congress and several former Reagan advisers, pledged their ''best efforts'' to defeat a tax bill that would raise $98.5 billion in revenues over the next three fiscal years. Mr. Reagan accepted the tax increases as part of a budget compromise earlier this year, and Wednesday the President expressed strong backing for the legislation, which is now being debated by a House-Senate conference committee. ''In the present weak economic climate,'' the conservatives said in a statement today, ''and during a time in which the Congress refuses to support the spending cuts required by the budget resolution, we friends and supporters of Ronald Reagan oppose the tax increase now before the House-Senate conference. We believe that to restore the health of the economy and put Americans back to work, America should follow a course against high taxes and Federal spending.''

''A Midsummer Night's Dream,'' The New York Shakespeare Festival's second dramatic offering of the summer at the Delacorte Theater in Central Park, is playing at 8 every night except Monday. James Lapine has directed the cast of 22, which includes William Hurt as Oberon. Tickets are distributed free, beginning at 6:15 P.M., to those who wait on line at the foot of the Great Lawn, at 80th Street in the park. Those who make financial contributions to the Shakespeare Festival are entitled to tickets without waiting. ''A Midsummer Night's Dream'' will run through Aug. 27. Performances are canceled if it rains. Information: 598-7100. NEWHALL PHOTOGRAPHS Beaumont Newhall's book ''The History of Photography'' is a classic in its field. And Professor Newhall, who worked as a librarian and curator at the Museum of Modern Art for 10 years, is a photographer as well as a historian. Fifty of his black-and-white pictures - landscapes, architectural studies and portraits of prominent photographer friends - are the subjects in ''Beaumont Newhall: Photography 1928-82,'' an exhibition that opens today at the International Center of Photography, on 94th Street at Fifth Avenue. The center opens daily at noon and closes today at 8 P.M. Tomorrow and Sunday the closing hour is 6 P.M. Admission is $2; students and the elderly, $1. Information: 860-1777.