Trying to decipher what actually happens when Congress passes a piece of major legislation is as complicated as trying to unravel the intricacies of a real estate scandal. With 535 members of Congress and their army of staff, the players are too numerous, the motivations too elusive and the deals too ephemeral for any observer to fully grasp what has happened -- and why.

Because of this thicket of complexity, identifying the motivations behind congressional behavior has become a favorite theme of political scientists trying to write their big book. The two leading academic theories of the 1970s were developed by Richard Fenno and David Mayhew. The former, through his detailed analysis of congressional committees at work, claimed that members of Congress were motivated by three factors -- the desire for reelection, the quest for power and prestige in Congress itself, and the dedication to framing good public policy. The latter took the more cynical tack and pointed to the desire for reelection as the preeminent motivation on Capitol Hill.

Now Rochelle Jones, a journalist, and Peter Woll, a professor of politics at Brandeis University, have collaborated on "The Private World of Congress," a book that takes on these ascendant theories in academic battle. They draw their battle lines early, stating in the preface, "In Congress, the ultimate prize is power and status on Capitol Hill." And they add in case the Mayhew-ites have not gotten the point, "Political scientists are, of course, aware that the internal power incentive exists but they continue to picture Congress as an institution primarily shaped by the members' drive for reelection."

The resulting book is alternately stimulating and tedious and, in the end, Jones and Woll fail to prove their argument. Almost all their examples involve Byzantine turf battles among Capitol Hill powers such as Sens. Russell Long (D-La.), Warren Magnuson (D-Wash.), Howard Cannon (D-Nev.), Edward Kennedy (D-Mass.) and former congressional health czar Paul Rogers (D-Fla.). These familiar figures can worry about power within Congress because they combine long service with relatively safe seats.

Sometimes, Jones and Woll bend the truth in an effort to dispute standard political motivations. For example, they argue, "It is a simple fact of political life that once a member has been elected, he has little cause to worry about reelection. This, holds equally true for congressmen and senators." This is certainly news to the five liberal Democratic senators who were defeated last year. In fact, the new 1980 edition of "The Almanac of American Politics" states clearly, "in 1976 and 1978 most of the senators who had serious challenges lost.

Jones and Woll also err in down-playing the actions of congressional newcomers -- particularly the large crop of House Democrats elected in 1974. True, they do detail how one of these junior Democrats, Rep. Andy Maguire (N.J.), used his congressional staff as a public-relations firm to cement his reputation as an energy expert. They claim Maguire's goal was prestige within Congress, noting that other congressmen were "impressed" to see a Maguire piece on the op-ed page of The New York Times. One suspects that this article was written to impress Maguire's northern New Jersey constituents, not Tip O'Neill and Al Ulman, particularly since Maguire has never has an easy election, winning in 1978 with only 53 percent of the vote.

There are, however, fascinating nuggets buried in these pages. For example, there's a description of the bitter fight over the 1977 tax bill in the Senate, in which Finance Chairman Russell Long clipped the wings of Ed Muskie's (D-Me.) newly created Budget Committee. As a result of the confrontation, the authors say, "In 1978 Muskie, despite his aggressiveness and combativeness, was still on the fringes, still lusting after power that was not quite within his grasp."

These journalistic touches, obviously the fruit of some non-academic interviews, are the book's strength. The writing is choppy, however, and all too often points are supported with long and not terribly illuminating extracts from the "Congressional Record" and hearing transcripts.

If "The Private World of Congress" is marred by too much theory, then "On the Hill" by Alvin M. Josephy Jr. suffers from the absence of any overriding theme. This 390-page history of Congress has all the bite of a high school American history text book. Orignally published in 1975 as the "American Heritage History of the Congress of the United States" and now updated, "On the Hill" fails to reproduce the strengths of the "American Heritage" approach to history. Only in discussing the first few sessions of Congress in the 18th century does Josephy provide the kind of colorful detail, often considered beneath serious scholars, that can convey the flavor of a period to the non-specialist.

By the time Josephy gets to the 1812, the great-man theory of American history takes over and the names and dates rush by in mind-numbing fashion. Occasionally, he stumbles on the little-known fact, such as that it took the Senate unitl 1921 to abolish its committee on Revolutionary War claims. But such asides are few and far between.

There is something fundamentally wrong with a history of Congress that begins with giants such as James Madison and ends with a pedestrian quote from William Cohen, currently the junior senator from Maine.