National Acid Deposition Control Act of 1984 - Title I: Acid Deposition Control and Assistance Program - Amends the Clean Air Act to direct the Administrator of the Environmental Protection Agency (EPA), within four months after the enactment of this Act, to compute a State share for each of the 48 contiguous States of a 10,000,000 ton reduction in annual emissions of sulfur dioxide by 1993 below that of 1980. Sets forth a formula for determining State shares.

Permits States to reallot shares among themselves if the required total reduction in annual emissions of sulfur dioxide is still achieved.

Sets deadlines and procedures for submission and approval of State plans for such State shares. Directs the Administrator to promulgate a State plan in the absence of a State submitted Administrator-approved plan.

Requires State plans to provide for emission limitations applicable to any existing stationary sources in the State for which the actual annual sulfur dioxide emission rates have been calculated by the Administrator for the calendar year 1980. Requires that the emission limitations for each stationary source subject to the State plan establish an allowable average annual sulfur dioxide rate at a level such that the total reduction would equal the State share.

Permits State plans to provide for compliance with emission limitations through use of fuel having a lower sulfur content than the fuel used in 1980, precombustion removal of sulfur (such as coal washing), technological systems of continuous emission reduction, or any other means which the State deems appropriate.

Authorizes the Administrator to commence a civil action for permanent or temporary injunction or to assess and recover a civil penalty of up to $25,000 per day of violation, or both, whenever any person violates any requirement in effect under this Act.

Eliminates a percentage reduction requirement with respect to sulfur dioxide emissions from any fossil fuel fired stationary source which: (1) commences construction after the date of enactment of this Act; and (2) complies with a standard of performance which prohibits sulfur dioxide emissions in excess of 1.2 pounds per million Btu.

Title II: Control of Nitrogen Oxide Emissions - Directs the Administrator to revise standards of performance for new stationary sources for emissions of nitrogen oxides from electric utility steam generating units which burn bituminous or subbituminous coal and which commence construction after the enactment of this Act. Prohibits the emission of nitrogen oxides from such units at a rate which exceeds: (1) 0.30 pounds per million Btu, in the case of subbituminous coal; and (2) 0.40 pounds per million Btu, in the case of bituminous coal.

Establishes nitrogen oxides emissions standards for light-duty trucks after model year 1986.