The heat wave that has given Washington a kind of warm-up for the official start of summer went into its fourth day yesterday, as pedestrians sought shade, householders turned up the air conditioning and the mercury climbed to 92 degrees.

The 92-degree reading, recorded at National Airport at 1:38 p.m., matched Friday's high temperature, and is the highest registered here this year.

Relief from the four consecutive days of 90-degree readings, a hot spell reminiscent of some of summer's worst, is expected today. National Weather Service forecasters predicted that today's highs would not climb out of the pleasant 70s.

So far this year, with summer not scheduled to open until June 21, Washington already has experienced seven days with temperatures of 90 degrees or above, the figure many area residents regard as characteristic of summer's worst.

On May 7 the mercury reached 91. On May 17 the reading was 90, and the next day the figure was 91. The heat wave began Thursday, with a 91-degree high temperature at the airport. After Friday's 92, came Saturday's 91.

All the days seemed noticeably hot, but none seriously threatened the all-time high for June 1 of 97 degrees, set 91 years ago.

In Baltimore readings of 97 yesterday and 96 Friday and Saturday all set or tied records.