President Reagan's veto of a $428 billion emergency spending bill will have a salutary effect if it keeps the issue focused on the complicated US government budgeting process - and not just the politics involved in the matter of whether Congress made the right ''mix'' of cuts to meet specific reductions sought by the White House.
That both Mr. Reagan and Congress are locked in a test of political wills is hardly surprising, given the ideological differences between a Republican White House and a Democratic House, as well as sharp institutional cleavages stemming from a Congress that has sought to assert its independence from all presidents during the past decade.
But what is fundamental in the current drama, it would seem, is two-fold: First, neither the White House or Congress must let the vital services of the federal government grind to a halt because of their momentary impasse. Second, it is imperative that budgeting by ''continuing resolution'' not be allowed to become institutionalized.
Having noted that, however, it is also clear that both parties to the dispute must share the blame in the current brouhaha. According to terms of the landmark Budget Act of 1974, which sets the deadlines for the budgeting process, Congress is supposed to complete all appropriation bills by the seventh day after Labor Day, with action on a second budget resolution to be finished by Sept. 15. Congress had completed action on only one appropriations measure going into the past week - a measure that funds Congress itself. The White House, for its part, had not sent along its revised budget requests until late September, thus inhibiting action in the Senate.