Although its progress across the skies was obscured here yesterday by dark clouds that produced rain, sleet, snow and widespread doubt, the sun nonetheless climbed steadily toward its Monday rendezvous with the vernal equinox and spring.

The National Weather Service announced that the official end to what has been for many a winter of cold, snow, slush and misery will arrive here at 6:34 p.m., March 20.

More important perhaps, there will be no meteorological credibility gap on Monday, according to forecasters. It will not only be spring in fact but spring in temperature, with the mercury rising to the mid 50s Monday.

For the next two days, however, comfort may require faith, hope and winter clothing.

Temperatures today are not expected to rise above the low 40s. Clouds will obscure the sun much of the time, and a northwest wind averaging 20 miles an hour should do much to enhance the impression that the chill of winter will never leave.

On Saturday, forecaster George Schielein said, the schedule calls for more sun and less wind, but temperatures remaining in the low 40s, well below normal.

Sunday should provide a passage into spring, with temperatures rising to the 50 degree levels expected for Monday, Schielein said.

yesterday was another kind of day entirely. In apparent defiance of any rules of seasonal logic, Tuesday's 64 degree temperature and Wednesday's splendidly sunny 58 were succeeded yesterday by temperatures in the 30s and 40s, stiff 20-mile-an-hour winds and a couple of inches of snow in upper Montgomery County.

Indeed, snowflakes and ice pellets mingled with the more numerous raindrops in the skies over downtown Washington, showing those who peered from office windows a sample of almost every type of precipitation winter can produce.