The President's `bargaining budget' proposes to spend $974 billion -- and leave a $180 billion deficit. For the first time since 1981, Mr. Reagan is asking for major cuts in programs that affect the middle class. Social security remains intact; defense outlays grow. 1.Politics of the budget: President's concern over deficit ranks behind defense buildup, domestic cuts. Story, below.(page 1) 2.`Hanging tough' on defense: Administration's request for hefty increase reflects past success in getting more. Page 3. 3. More social-program cuts: Trims now extend to middle-class benefits, but social security monolith stays intact. Page 3. 4. Budget prospects in Congress: Despite protests from the Hill, chances for this budget are better than in past. Page 4.