The heaviest March rains in Massachusetts history will raise the Charles eight feet above flood level by Friday, the Massachusetts Civil Defense office said last night.

The U.S. Weather Bureau issued emergency Flash Flood warnings late last night as the swollen river--already running three to four feet above flood level in many areas--began to cause minor flood damage near Needham.

By Friday, the Charles will overflow its banks and threaten "severe flood damage" in several areas near Needham, Civil Defense authorities said last night.

The outlook for Cambridge is still unclear. The Metropolitan District Commission predicted last night that the river would not overflow its banks in Cambridge, and that Memorial Drive and Soldiers' Field Road will probably remain open.

But the MDC can make no definite prediction, it said, until it sees the extent of upstream flooding. "We just don't know what it's going to do to us until we see what it does in Needham," an MDC official said.

The Weather Bureau said that the 4.75 inches of rain that had fallen by 9 p.m. yesterday was an all-time 24-hour record for Boston. The storm also set a record for March rainfall here.

The rains will taper off this afternoon as the storm moves out to sea, the Weather Bureau said. But run-off from small rivers will keep the Charles rising until it hits its crest sometime Friday night.

So far the rain has done little damage in Cambridge. Cambridge Police said last night that the rain had been "remarkably harmless." Traffic kept moving, they said, and no major intersections or underpasses were flooded.

Damage so far at Harvard has also been light, the Buildings and Grounds department said yesterday. "There have been a lot of leaks and a few flooded cellars," one B&G official said, "but hell, that happens every time it rains."

Cambridge Police maintained their proper sense of perspective throughout the crisis. "I'd sure hate to think what would happen if the river rose eight feet," one sergeant said. "I'd sure hate to see Harvard float out to sea."