The Washington area's first air pollution alert of the year was extended for a second day yesterday by the Metropolitan Washington Council of Governments, although yesterday's smog levels were reported to be only moderately high.

Photochemical smog, the area's main pollutant during the summer, rose to a high of 65 on COG's air quality index at 4 p.m. at the agency's monitoring station in Alexandria, a level officially termed "unhealthy."

Air pollution alerts normally are announced only when pollution levels reach or exceed 100 on COG's index. COG officials said yesterday that they had extended the alert because stagnant air had been forecast to remain over the Washington area today, raising prospects of relatively high smog levels.

The Transportation Planning Board, a regional agency affiliated with COG, met yesterday to take preliminary action on a series of controversial antipollution measures, primarily designed to curtail auto travel in the Washington area.

Photochemical smog, which consists chiefly of ozone, is caused mainly by automobile exhausts. Smog, also known as a photochemical oxidant, is formed when a chemical reaction takes place in the presence of sunlight between hydrocarbons and nitrogen oxides, both of which are hyproducts of auto exhausts.

Carbon monoxide, another major pollutant in the Washington area, especially during the winter, is also produced by auto combustion.

The Transportation Planning Board agreed to consider during the next few months a range of antipollution on free or low-cost parking for federal employes, higher gasoline or other taxes, additional on-street parking bans for commuters and mandatory annual auto inspections to force motorists to pay for car repairs if their autos emit excessive pollution.