An air pollution alert for the Washington area was extended 24 hours yesterday afternoon, but officials expressed hope for more breathable air later this weekend with possible arrival of a week cold front moving in from the west.

The Metropolitan Washington Council of Governments air quality index dropped slightly from Thursday's 130 to 100, still a "very unhealthy" reading, causing the pollution alert to be extended at 3 p.m.

The alert remained in force despite severe thundershowers that brought torrents of rain to parts of the area last night. A National Weather Service forecaster said that the storms would clear away some of the smog, but would not greatly affect the overall weather picture.

Additional showers are predicted today, and these might again give localized relief, but "for real improvement we have to look toward this week cold front," a forecaster said. "If it gets here (Saturday) afternoon, it may help to clear things out."

The pollution alert began Thursday as the result of a stagnant air mass over eastern Canada that kept automobile emissions from dispersing. Krause said sumer sunlight triggers the problem: "It's not strong enough in winter to cause the photochemical reaction" between the auto emissions and light that produces the eye-stinging zone experienced here this week, he said.