Democrats scored major gubernatorial victories in two key states yesterday as state Treasurer Ann Richards came from far behind to defeat maverick oilman Clayton Williams (R) in Texas, while former senator Lawton Chiles toppled a Republican incumbent to win in Florida.

But Republicans seized the Ohio governorship from the Democrats as former Cleveland mayor George Voinovich rebounded from a decisive Senate defeat in 1988 to defeat Attorney General Anthony Celebrezze (D). And another Republican, former Justice Department prosecutor William F. Weld, defeated Boston University President John R. Silber (D) in Massachusetts by a small margin, with Silber conceding shortly before 2 a.m.

Other governor's races remained remarkably close early this morning, with Democrats in position to topple the Republican incumbent in Nebraska and the GOP in Minnesota threatening to oust the Democratic incumbent with a nominee who had been on the ballot only nine days. Contests in Michigan and Maine also were cliffhangers.

In Michigan, incumbent James J. Blanchard (D) was holding slim lead over Senate Majority Leader John Engler (R) with 87 percent of the vote counted, with many of the outstanding ballots in the predominantly Democratic Detroit area.

In Illinois, Secretary of State Jim Edgar (R) appeared to have defeated Attorney General Neil F. Hartigan (D) with 94 percent of ballots counted.

And in the contest for the crown jewel of the 36 gubernatorial races at stake, Sen. Pete Wilson (R) led former San Francisco mayor Dianne Feinstein (D) in early California returns. Most of these ballots were filed by absentee voters who had been expected to favor Wilson, and a network exit poll of those who voted yesterday showed a virtual dead heat.

One of the most surprising Democratic victories occurred in Kansas, where state Treasurer Joan Finney (D), a strong opponent of abortion, upset first-term Gov. Mike Hayden (R), whose candidacy was hurt by raising taxes.

In Austin, Richards told a cheering crowd that her victory was "based on the power of the people, not the power of money."

Williams asked his supporters not to boo as he conceded the race. "It's not the end of the world," he said in Austin. "I did my best." As supporters chanted "'94! '94!", Williams replied: "I'm an Aggie, but I'm not crazy."

Richards's dramatic upset was a personal blow to President Bush in his adopted home state. Bush spent the last three days before the election campaigning there for Williams, who was damaged by a series of blunders, including his admission that he paid no federal income tax in 1986.

Gubernatorial races are especially important this year because they will help to determine which party has the advantage in congressional redistricting.

As many as 20 to 25 House seats could change parties in California and Florida alone, perhaps enough to determine whether a conservative or liberal majority is dominant in the next several years.

Democrats had a significant advantage in the redistricting battle as incumbents Mario M. Cuomo (D) in New York and Robert P. Casey (D) in Pennsylvania cruised to easy victories in states that stand to lose several congressional seats. The only drama in New York was the race for second place, in which economist and political amateur Pierre Rinfret (R) appeared to edge Conservative nominee Herbert London.

One unusual development involved two independent candidates. Former Republican senator Lowell P. Weicker Jr., who led from the start, won the three-way Connecticut governor's race, while former governor and interior secretary Walter Hickel was favored to win in Alaska.

In Alabama, first-term Gov. Guy Hunt (R) defeated Paul Hubbert (D), former head of the state teachers' union, whom Hunt assailed for supporting gay teachers and tried to link to Jesse L. Jackson.

The Democratic victories in Texas and Florida, if buttressed by a Feinstein win in California, would place the party in strong position to influence redistricing in the three states.

They could gain 14 new House seats. Chiles, who ran a low-budget, populist campaign, ousted first-term Gov. Bob Martinez (R), who was hurt by his antiabortion stance and a flip-flop on raising taxes.

In Massachusetts, Weld, a wealthy, moderate Republican who quit the Justice Department to protest the conduct of then-Attorney General Edwin Meese III, rallied late in the campaign to overtake Silber, the outspoken academic who had defeated two veteran Democratic politicians.

Both sought to tap public anger at outgoing Gov. Michael S. Dukakis (D).

Several states were considered too close to call. Ten-year incumbent Minnesota Gov. Rudy Perpich (DFL) was narrowly trailing state auditor Arne Carlson, who became the last-minute GOP nominee when Jon Grunseth dropped out after allegations that he went skinny-dipping with teenage girls a decade ago.

In Vermont, former governor Richard A. Snelling (R) defeated former state senator Peter Welch (D). In Maine, with 77 percent counted, first-term incumbent John R. McKernan Jr. (R) held a slim lead over another former governor, Joseph E. Brennan (D).

In heavily Republican Nebraska, Gov. Kay Orr (R), who apologized for breaking her pledge not to raise taxes, narrowly trailed wealthy attorney Ben Nelson (D) with 93 percent of ballots counted.

Democrats retained the governorship in Oregon, where Secretary of State Barbara Roberts (D) defeated Attorney General Dave Frohnmayer (R).

In Arizona, with 53 percent counted, former Phoenix mayor Terry Goddard (D) was leading real-estate developer Fife Symington (R).

Abortion was a key issue in several states, including Florida and Ohio, where Celebrezze failed to catch Voinovich despite pushing his new-found pro-choice stance.

In the South, most governors were headed toward easy reelection, with Democrats leading the open contests.

While little attention has been paid to lightly contested elections, the outcomes reflected the complexity of partisan politics in the rapidly changing region. Democrats are solidly entrenched in some states, and Republicans are on the verge of achieving near, if not full-scale, realignment in others. For example:In South Carolina, Gov. Carroll A. Campbell Jr. (R) coasted over his black challenger, state Sen. Theo Mitchell (D), who repeatedly expressed anger at members of his party, black and white, for failing to back his campaign.

The GOP has a decisive 2 to 1 advantage over the Democratic Party in voter identification among whites and could, by the end of the decade, control the once solidly Democratic state. In Tennessee, which 20 years ago was moving strongly toward GOP control, Gov. Ned McWherter (D), a 280-pound, cigar-smoking poker player, routed Dwight Henry (R), a freshman state representative, and Democratic control of the legislature remained firm. In solidly Democratic Arkansas, Gov. Bill Clinton (D) easily beat Sheffield Nelson, a businessman and novice nominee, and his victory margin appeared strong enough to keep him on the list of potential competitors for the Democratic presidential nomination. In Georgia, Lt. Gov. Zell Miller (D), an advocate of a state lottery, beat House Minority Leader Johnny Isakson (R). In Oklahoma, Democrats regained the governorship as businessman David Walters (D) defeated Bill Price (R), a former U.S. attorney.

In the Mountain West, most gubernatorial contests did not involve serious challenges. Many Democrats coasted to victory in states where the Republican Party is dominant in presidential and most local elections.

Incumbent Democrats who won decisively were Colorado's Roy Romer, who defeated John Andrews, president of the conservative Independence Institute and a dabbler in parapsychology, and Idaho's Cecil D. Andrus, who had been challenged by state Senate Majority Leader Roger Fairchild.

Nevada's Robert J. Miller defeated businessman Jim Callaway, and Wyoming's Mike Sullivan brushed aside the bid of Mary Mead, president of the Wyoming Heritage Society and daughter of former governor and senator Clifford P. Hansen.

In New Mexico, former governor Bruce King (D) defeated former state representative Frank Bond (R).

Other lopsided races included:Iowa, where antiabortion incumbent Terry E. Branstad (R) easily defeated House Speaker Don Avenson (D), an abortion-rights supporter. South Dakota, where Bob Samuelson (D) gave Gov. George S. Mickelson (R) little to worry about in his bid for another term. Hawaii, a solidly Democratic state where former world surfing champion Fred Hemmings (R) never caught a wave in his bid to oust Gov. John D. Waihee III (D). New Hampshire, a GOP bastion where Gov. Judd Gregg (R) easily defeated state Democratic Party Chairman Joe Grandmaison. Rhode Island, where businessman Bruce Sundlun (D), who had run twice, coasted to victory over Gov. Edward D. DiPrete (R), whose negative ratings were close to setting records in the economically depressed state. Wisconsin, where conservative, tough-talking Gov. Tommy Thompson (R) easily won a second term in his race against House Speaker Thomas Loftus (D).

Contributing to this report were staff writers David Maraniss in Austin and Jay Mathews in Los Angeles, special correspondent Christopher B. Daly in Boston and staff researcher Ralph Gaillard Jr.