House Democrats on Tuesday unveiled a $3 trillion pandemic relief measure, an ambitious package with aid for struggling states and another round of direct payments to Americans that Republicans instantly dismissed as an exorbitantly priced and overreaching response to the coronavirus crisis.  The proposal, which spanned 1,815 pages, would add a fifth installment to an already sweeping assistance effort from the federal government, although its cost totaled more than the four previous measures combined. And unlike those packages, which were the product of intense bipartisan negotiations among lawmakers and administration officials who agreed generally on the need for rapid and robust action, the House bill represents an opening gambit in what is likely to be a bracing fight over what is needed to counter the public health and economic tolls of the pandemic. It included nearly $1 trillion for state, local and tribal governments and territories, an extension of unemployment benefits and another round of $1,200 direct payments to American families.