They dyed the Chicago River green today, painted a green stripe down Dearborn Street and sent legions of city workers into the streets with signs proclaiming, "Use Your Brain, Vote For Jane" and "Write-in Byrne for Mayor."

But it was clear that Mayor Jane M. Byrne's write-in campaign for reelection was off to a lukewarm start as she led a colorful St. Patrick's Day parade through the Loop.

Wearing a bright green beret and carrying a black walking stick, the tiny Irishwoman was greeted by as many boos as cheers as she marched down Dearborn Street, and when she took her place at a reviewing stand Democratic Party leaders were noticeably absent.

The heavily Irish crowd gave Rep. Harold Washington (D-Ill.), a black preacher's son who beat Byrne and State's Attorney Richard M. Daley in the primary, and Bernard E. Epton, the Republican Party's Jewish nominee, at least as warm a reception as it did Byrne, who threw the Democratic Party and the Chicago mayoral race into turmoil Wednesday by announcing she would seek reelection as a write-in candidate.

The announcement of Byrne's write-in campaign dumbfounded Democratic Party leaders here, and the mayor was described in Chicago newspapers today as "Baby Jane," "Crybaby Jane," "Mayor Bossy," and "a profound embarrassment to the city."

Byrne reenters the race as a lone wolf. Most of her former supporters, including campaign manager Bill Griffin, have deserted her. Not a single party leader has endorsed her candidacy.

However, she reportedly has about $1 million left in the $10 million fund she raised for her election, and her position as mayor guarantees her major attention.

House Ways and Means Committee Chairman Dan Rostenkowski (D-Ill.) underscored the displeasure of party leaders with Byrne by endorsing Washington for the first time today.

"Jane Byrne's write-in campaign mocks every voter in Chicago," the colorful Chicago congressman said in a prepared statement. "She has placed herself above the traditional rules of politics. She flies the flag of a spoiler. And she should be treated as one."

Byrne's former black supporters spoke even more harshly of her.

"This is a blatant racist action," Alderman Robert Shaw said in an interview today. "The black community sees no difference in what she is doing and what George Wallace did when he stood in the schoolhouse door and kept blacks from entering."

The conventional political wisdom here is that Byrne's write-in effort benefits Washington because it rallied Democratic leaders, previously cool to his candidacy, and is expected to divide the white vote.

Washington won the bitter three-way Democratic primary with only 36.3 percent of the vote, with most of his support coming from blacks. About 400,000 of the 1.2 million voters expected to participate in the April 12 general election are black.

Epton conceded that Byrne's entry into the race will hurt his candidacy, and placards appeared at one of his rallies saying "A Vote for Byrne Is a Vote for Washington."

National Democratic leaders, extremely concerned about Washington's candidacy, have launched an unprecedented drive to raise money for him and to shore up his support among white Democrats by sending a host of party leaders to campaign for him.

These include Sen. Edward M. Kennedy (D-Mass.), who endorsed Byrne in the primary; former vice president Walter F. Mondale, who endorsed Daley in the primary, and former senator and secretary of state Edmund S. Muskie.

The fear, according to Democratic National Committee political director Anne Lewis, is that blacks, who have become the party's most dependable voting bloc, will become disillusioned if white Democrats don't vote for Washington, the first black to win a mayoral nomination here.

Washington, who jostled his way to the front of the 131-unit parade so he could march directly behind Byrne, was symbolically accompanied by two leading Democrats, Cook County Board President George Dunne and Illinois Attorney General Neil Hartigan, and a Roman Catholic priest, the Rev. George Clements.

Washington blew kisses to the crowd of thousands as he walked. He insisted he belonged at the head of the parade because "I've won this thing."

Among the most often-voiced concerns are that Epton may drop out of the race, propelling Byrne back into contention. Epton emphatically denies any such intention.