To the unaccustomed throb of mariachi bands, the bitter, three-year struggle between Democratic Mayor Harold Washington and his party's white-dominated machine for control of City Hall hits a new crescendo next week when inner-city voters elect aldermen in seven redistricted City Council wards.

Tuesday's special election could put vast patronage powers firmly in Washington's hands by giving him a council majority for the first time since he took office in 1983 as a self-styled reformer.

Or it could cement his status as a uniquely weak leader in Windy City annals, lacking enough clout to overcome entrenched opponents led by Alderman Edward R. Vrdolyak. The Cook County Democratic chairman controls 29 votes on the 50-member council to Washington's 21.

Perhaps equally important, new Hispanic aldermen will be elected in three wards, replacing old-line whites and raising the number of Hispanic aldermen to four. In those wards, both sides are backing their own Hispanic candidates, recognizing that the day approaches when this historially weak but fast-growing ethnic group of about 600,000 can exert political clout.

The results will be read by this city of political hardball fans as a harbinger of the 1987 mayoral election, when the machine seems certain to oppose another four-year term for Washington.

These issues triggered intense politicking after a federal court last year ordered a redistricting of the wards in the economically depressed West Side and Southwest Side. Plaintiffs had argued that gerrymandering after the 1980 U.S. census denied the vote to thousands of Hispanics and fewer blacks.

In recent days, Washington and Vrdolyak have visited these often-neglected neighborhoods, where jobless rates are triple the national average and families in the tar-paper-roofed duplex townhouses called "two-flats" here look out on streets of struggling businesses, while gangs and drug dealers prowl trash-filled alleys.

With fierce accusations of misconduct flying back and forth, and numerous reports of window-smashing and other vandalism to candidates' campaign offices, forces for Vrdolyak and the mayor are campaigning hard for their slates, gobbling spicy delicacies, cavorting in sombreros, applauding the mariachis and soul singers.

Both camps publicly boast of taking four or five wards, while insiders privately predict that they each will take three wards, with an unpredictable race is one of the new Hispanic districts.

Chicago's Hispanics won their first council seat just three years ago. Freshman Alderman Miguel Santiago votes with the white majority opposed to Washington.

At first glance, the risks Tuesday seem higher for Vrdolyak, because seven of his loyalist aldermen have been redistricted.

Three remapped wards are in predominantly black neighborhoods represented until now by whites. The four other new wards encompass mostly Hispanic and black communities, with Santiago representing one and whites the others.

Three of the incumbents, including Santiago and two whites, are seeking reelection; three will run for other offices. The seventh remapped alderman, Vito Marzullo, 88, is retiring.

If Washington's forces win four of the seven new seats, the mayor gains a 25-to-25 council tie with Vrdolyak -- and he holds the tie-breaking vote. A one-vote majority would allow him to install scores of long-stalled key appointees, replacing machine veterans.

But loose organization, lack of funds and continuing repercussions from a federal probe into possible bribe-taking by some Washington appointees have taken their toll. Washington's effort was late starting, and Vrdolyak's cadres are well-financed and experienced.

Chicago has a diverse Hispanic population, with 369,000 Mexicans, 127,000 Puerto Ricans, 18,000 Cubans and 67,000 Hispanics of "other" heritage, each group with its own aspirations, fears, envies and heritage.

Such differences work against the possibility that the newly elected Hispanics could easily become a powerful faction, bartering crucial votes with Washington or Vrdolyak for greater patronage.

The heart of the battle is control of traditional patronage powerhouses, such as the Chicago Park District, the Regional Transit Authority, the City Colleges board and other fiefdoms.

The Vrdolyak-controlled council has bottled up 47 mayoral appointments to these boards, commissions, and panels. Each of these quasi-independent agencies annually hands out thousands of part-time, seasonal and non-Civil Service patronage jobs.

The Park District, long run by Edmund Kelly, who has ties to the family of the late mayor Richard J. Daley and the machine, has an annual budget of $270 million and more than 3,000 employes, plus thousands of part-timers.

Other patronage powerhouses include: the Regional Transit Authority, ($486 million budget this year, 1,400 employes); Chicago Transit Authority ($614 million, 12,000 employes); City Public Buildings Commission ($106 million, 185 employes); City Colleges Board, ($222 million, 8,000 staff).

Shifting allegiances make the election outcome uncertain. In the redrawn West Side 25th Ward, state Rep. Juan Soliz, who won a 1983 General Assembly seat with Washington's backing as an antimachine candidate, is running for alderman with Vrdolyak's support and is seen as the front-runner. Washington backs Juan Velasquez. The result may turn on Virginia Martinez, gaining strength as a nonaligned alternative.

Meanwhile, the patronage issue charges the showdown with extra tension. Washington "could knock Ed Kelly out of the Parks in a minute" if he gains a majority vote, said one Vrdolyak stalwart.

"Vrdolyak's people are going to be out there fighting, because these boys understand what's at stake," a top mayoral aide said. A runoff will be held April 29 in wards where no candidate tops half the vote.

The Chicago election has all but eclipsed the statewide primary, where state Rep. Judy Koehler faces steel executive George Ranney for the Republican nomination to oppose Democratic U.S. Sen. Alan J. Dixon this fall.