Geneva Overholser's ire at sport utility vehicles [op-ed, May 28] echoes the arguments used to make Americans feel guilty about driving -- namely, that our vehicles "spew pollution and guzzle gas." A few related facts might eliminate the guilt trip that some activists want motorists to take.

First, the air is significantly cleaner than it was just a decade ago. According to the Environmental Protection Agency, the nationwide average of poor air quality days reported in our largest cities was 50 percent lower in 1991-1995 than in the previous five years. In addition, the major air pollutant emissions have fallen by 30 percent since 1970. By incorporating advanced technologies to build cleaner vehicles and produce cleaner fuels, highway transportation has contributed the lion's share of this dramatic clean air progress.

Second, while Americans are driving more than ever (annual vehicle miles of travel have increased 130 percent since 1970), fuel consumption rates have dropped significantly because of advances in automobile engineering. According to the Federal Highway Administration, Americans get an average of 21.5 miles per gallon in cars and 17 miles per gallon in all motor vehicles combined today. Those numbers compare with a nationwide average of 13.5 miles per gallon for cars and 12 miles per gallon for all motor vehicles in 1970.

WILLIAM D. FAY

Washington

The writer is president and CEO of the American Highway Users Alliance.

Geneva Overholser's polemic about sport utility vehicles proves the point I was trying to make: Debate on global warming is centered on how best to regulate and divide what is perceived to be the shrinking pie of world resources. Such politics of scarcity lends itself to emotionally charged and not terribly productive exchanges.

America has the capacity to change the dynamics of the environmental debate through development of biological engineering techniques for producing fuels, chemicals and materials from almost anything growing or that has grown (known as biomass), while at the same time contributing to the cleanup of our atmosphere.

Contrary to Ms. Overholser's assertion, new proposals by the Clinton administration on SUVs will do little to alleviate greenhouse gas emissions that threaten global climate stability. The act was written to control urban smog, not global warming. Although catalytic converters have been effective in reducing ozone levels, the Environmental Protection Agency now fears the devices are a growing cause of global warming by increasing nitrous oxide emissions.

By contrast, bio-based fuels, such as ethanol, have potential to be sustainable, low-cost and high performance, are compatible with current and future transportation systems and provide near zero net greenhouse gas emissions. Promoting biomass conversion technologies will provide a new and sustainable resource consisting of weeds, agricultural waste, even the lowly kudzu vine, for the production of fuels and chemicals.

RICHARD G. LUGAR

U.S. Senator (R-Ind.)

Washington

The writer chairs the Senate Committee on Agriculture, Nutrition and Forestry.