The Beltway is no longer a barrier against the pitfalls of a down economy. The majority of Wash­ington’s top-grossing law firms saw revenues slide in 2009, and 2010 isn’t shaping up to be a strong year either, firm leaders say.

The National Law Journal D.C. 25 survey, our annual ranking of the top money-makers among Washington law offices, found that, for the first time in 11 years, the combined gross revenue for Washington’s largest firms declined, falling 2.7% to $5.9 billion. In all, 17 Washington offices reported decreases in their revenue last year compared to seven in 2008. Put another way, Washington’s largest firms lost more than $163.9 million in 2009 — roughly the same amount a firm the size of O’Melveny & Myers collects in D.C. Many firms were able to keep their profits per equity partner in the black by reducing headcount. Even then, overall PPP was down 0.5% to $1.27 million.