The death of Mr. Washington, who was beloved in black neighborhoods here and bitterly disliked in most white wards, stunned supporters and foes alike in the city. Groups of strangers gathered on sidewalks to share the news and, sometimes, to wipe away tears. Jackson Cuts Short Trip

''When I was young, we never dreamed there'd be a black Mayor of Chicago someday,'' said Ollie Hawkins, a 73-year-old retired department store salesperson, who stood with the throngs of curious onlookers outside Northwestern Memorial. ''We're going to miss Harold.''

The Rev. Jesse Jackson, the Democratic Presidential candidate who was recently endorsed by Mr. Washington, cut short his trip to the Persian Gulf to attend the funeral, details of which had yet to be announced.

Mr. Washington, who often said he intended to serve as Mayor for five terms, did not believe in grooming a successor, his aides said.

''That was the last thing on his mind,'' said Ernest Barefield, the Mayor's chief of staff. ''He fully intended to be Mayor for 20 years.'' 'In Rare Form'

Timothy Evans, the Mayor's floor leader in the City Council, is considered to have the best chance of becoming Acting Mayor. Mr. Evans, who is black, has served on the Council since 1973, and has been generally popular, even among Mr. Washington's detractors.

Speaking at a news conference after the Mayor's death, Mr. Evans said Mr. Washington was ''in rare form'' earlier today in his last official act as Mayor, at a ground-breaking ceremony for low-income housing on the South Side.