The amount of lead in U.S. air continued to decline dramatically in 1986, and five other pollutants registered little or no change over the previous year, the Environmental Protection Agency reported yesterday.

In its annual air quality survey, the EPA said that the average level of lead in nationwide samples of air dropped 35 percent in 1986, the sharpest yearly decline for any pollutant since the agency began monitoring in the early 1970s.

Assistant EPA Administrator J. Craig Potter attributed the decline to the latest tightening of standards for lead additives in gasoline effective Jan. 1, 1986. Since the phase-out of leaded gasoline began in the mid-1970s, the agency has recorded an 87 percent decrease in atmospheric levels of the heavy metal.

Lead levels in the Washington area dropped by nearly 20 percent in 1986, bringing the area well within the federal air quality standard for the pollutant. Only a handful of major U.S. cities, in which lead industries are located, exceed the standard.

Once considered a danger confined to lead workers and ghetto children who eat chips of leaded paint, the metal has emerged as a major public health peril. Even small quantities in the blood are believed to cause learning disabilities in children, hypertension in men and pregnancy problems.

Most atmospheric lead comes from motor vehicles. In 1977, vehicles emitted 124,200 metric tons of the metal. In 1986, after nine years of the lead additive phase-out, vehicles released 3,500 metric tons into the air.

Potter called the improvement "truly remarkable." But he said the agency is still undecided whether to ban lead as an additive, as environmentalists urge.

Environmentalists said that the EPA's success in cleaning up lead shows the benefits of strong regulation, and they criticized the agency for not aggressively controlling other chemicals released into the air.

David Doniger, a spokesman for the National Clean Air Coalition, said that after a regulatory push in the late 1970s, "the steam has gone out of the system. We have to have another ratcheting down of standards."

As an example, he cited the EPA's report for five other air pollutants surveyed in 1986. Levels of sulfur dioxide declined 3 percent and ozone 2 percent, while nitrogen dioxide, carbon monoxide and particulates registered no change.

For the Washington area, the EPA recorded slight increases for particulates and sulfur dioxide, small decreases in carbon monoxide and nitrogen dioxide, and no change in ozone.

Nationally, advances in the control of ozone, nitrogen dioxide and particulates in the first half of the past decade have slowed markedly in the second half, the report shows.

Potter said the slowdown resulted from the industrial upturn of recent years and the steady increase in the number of motor vehicles.

The most intractable problem, he said, is ozone, which is the principal component of smog and which causes pulmonary and respiratory problems. More than 50 metropolitan areas containing 75 million persons exceed federal standards for the pollutant. Ozone is produced by a photochemical reaction of nitrogen oxides and hydrocarbons released from chemical factories, power plants and motor vehicles.

Since 1977, ozone levels declined 13 percent, but there has been only a 4 percent decrease in the past five years, according to the EPA report.

Legislation has been introduced that seeks to reduce tailpipe emissions of hydrocarbons and nitrogen oxides. Potter noted that the agency opposes such measures.