The Obama administration has sent lawmakers its plan for new regulations of derivatives, the complex financial instruments that played a major role in the nation’s economic collapse. The White House wants rules that would have a form of derivatives, credit default swaps, traded on public exchanges and backed by existing capital. But it hasn’t endorsed calls for an outright ban on derivatives linked to speculative trading. The administration’s proposal marks the last element of its overhaul of financial regulations. Lawmakers will consider the plan when they return from August recess.