Arguably the most powerful person in the increasingly bitter budget fight between Congress and the White House is not House Speaker J. Dennis Hastert (R-Ill.), Senate Majority Leader Trent Lott (R-Miss.) or even President Clinton.

Instead, it is a comparatively obscure congressional bureaucrat whose name is largely unknown outside the Beltway and whose agency occupies a single floor in a nondescript building near a noisy freeway on the fringe of Capitol Hill. Unlike the better-known budget players, Congressional Budget Office Director Dan L. Crippen shuns the spotlight and so dislikes the notion that he will play an outsized role in the battle that he refused to comment publicly for this article.

But at the end of the budget negotiations, it is Crippen and his army of number-crunchers who will comb through the bills, weigh the offsets and the gimmicks, and deliver the crucial verdict on whether Congress and the White House have in fact lived up to their strident pledges to never dip into the Social Security surplus to pay for their programs.

So far, CBO's numbers show that no one has honored that pledge and that the bills or proposals from all sides are on target to invade Social Security.

The CBO's judgment has major political ramifications--if one party can plausibly blame the other for "raiding" Social Security, they can then use that political hammer to bludgeon their opponents in next year's elections. Of all the parties in the budget process, only Crippen and the nonpartisan CBO have the credibility to say who is right.

Crippen, 47, defies the image of a wonkish bureaucrat. His towering height and full beard give him the look of a 19th-century mountain man, and his off-hours pursuits are hardly the hobbies of a budget nerd: He is a licensed electrician, an accomplished plumber and a private pilot who enjoys hunting and fishing.

A former Republican Senate and White House aide and lobbyist, Crippen has had a rocky tenure since he was appointed CBO's fifth director in February. At one time or another this year, the White House and congressional Democrats and Republicans have smarted under CBO's analyses and have lashed out at Crippen for what they say are biased analyses of their proposals.

Getting caught in the middle of a high-stakes budget fight is an uncomfortable but familiar role for the agency. Former director Robert Reischauer, a Democratic appointee, enraged the Clinton White House when CBO's assessment questioned the financing of Clinton's health care proposal in 1994 and ultimately helped Republicans sink it.

Congressional Republicans handpicked Reischauer's successor, June O'Neill, but they were similarly infuriated when O'Neill's estimates of the GOP's 1995 budget-cutting proposals questioned their potential savings.

Crippen was another Republican pick, but the former aide to Howard Baker (R-Tenn.), a onetime Senate majority leader and White House chief of staff, drew fire from conservative Republicans who thought he would take an insufficiently hard line on fiscal matters. Some Democrats, meanwhile, thought his post-Baker career as a lobbyist made him unfit for a job that previously had been filled by appointees from academia or the policy world.

So far, Crippen's numbers have given little comfort to either side. Based on the bills Clinton has signed or Congress has passed, CBO's analysis shows that both sides have exhausted the non-Social Security surplus and crossed the line into funds technically being set aside for Social Security.

Budget experts say this is an artificial debate, since both parties have willingly spent the Social Security surplus for decades without cutting benefits by a dime. They also note that trying to make precise estimates of the difference between spending and revenue in a $1.6 trillion budget is a fool's game, since no forecaster ever gets it exactly right.

That said, though, CBO's preliminary numbers show that the only hope Congress and the White House have to avoid touching Social Security money is to box in CBO by insisting that the agency performs its calculations with numbers that essentially preordain the outcome. Specifically, Congress or the administration could require CBO to work with spending projections from the White House's Office of Management and Budget rather than its own numbers. Some of OMB's estimates show programs spending money more slowly than CBO does, thus saving money in the next fiscal year.

In fact, Congress already has used this so-called "directed scoring" to shave $18.5 billion from its spending bills. Congress now could order CBO to make its final analysis by substituting OMB's spending assumptions for its own, which would help all sides steer clear of the Social Security funds. But CBO has vowed that if asked to do so, it will also include its own scoring estimates, which will likely show that all sides have invaded the Social Security surplus.

That, some observers say, makes it likely that congressional leaders will simply avoid asking CBO for a final analysis. Once congressional leaders and the White House have agreed to a deal, "the last thing they want at that point is their train to be derailed by green-eyeshade analysts," said Reischauer.