Members of Congress come and go, but their loyal staff members stay on and on -- at least until they go to work for big bucks off the Hill. Now, David H. Brockway, chief of staff of the Joint Committee on Taxation and probably the principal staff architect of the Tax Reform Act of 1986, is leaving to join a law firm.

The Joint Committee staff occupies a peculiar place in the congressional hierarchy, supplying technical expertise to tax-writing committees in the House and Senate -- and to reporters, on condition of total anonymity.

Former heads of the committee staff, nearly all of whom are now working for Washington law or accounting firms, have exercised considerable power over the years.

The politically savvy Brockway is no exception. It was his idea to propose a sweeping set of tax-shelter limits that formed one of the building blocks of the tax-revision law. And he sat behind closed doors night after night last year with Ways and Means Committee Chairman Dan Rostenkowski (D-Ill.) and then-Senate Finance Committee Chairman Bob Packwood (R-Ore.) attempting to reconcile the House and Senate bills.

Brockway was ardently pursued by several firms. He chose Dewey, Ballentine, Bushby, Palmer & Wood, where he will join former Ways and Means chief counsels John Salmon and Joseph K. Dowley and former Carter administration Treasury officials Lawrence O'Brien and John M. Samuels.

Will Brockway, like many former Hill aides, spend his days lobbying Congress?

Ever one to twist a metaphor, Brockway answers: "Everybody ends up coming back here, but that is not the bread and butter of what I want to do."