When Gov. William A. O'Neill (D) decided to retire rather than seek another term after raising taxes, he could not have guessed how wild the scramble would be to elect his successor. Rep. Bruce A. Morrison (D), who had announced against O'Neill, got the Democratic nomination, but has been unable to persuade O'Neill's friends to rally to his cause. Rep. John G. Rowland (R) could have won hands down, except that former senator Lowell P. Weicker (R) decided to run as an independent. An established name and a formidable personality, Weicker has dominated the campaign. In the closing week, Rowland began to chip away, mainly by questioning Weicker's financial dealings and official ethics in the Senate, and came up with enough money to make a late TV buy on New York stations that reach Weicker's Fairfield County base. Weicker has responded strongly and the betting is he will hold on.

The New Haven House seat Morrison is leaving is almost certain to go to Rosa DeLauro (D), a liberal activist, over conservative state Sen. Thomas Scott (R). The battle in Rowland's district has been much more intense as former representative Toby Moffett (D), another well-connected liberal, tries to overcome the "carpetbagger" label placed on him by rival Gary Franks (R), a Waterbury alderman. Franks is a black conservative businessman -- a new combination for the district -- and despite Rowland's home-district coattails, is the underdog. DISTRICT OF COLUMBIA

Two Democrats who have never held elective office are favored to win the top races. Sharon Pratt Dixon (D), who campaigned on a pledge to "clean house" after the 12-year administration of Mayor Marion Barry (D), faces Maurice T. Turner Jr. (R), a former police chief recruited to the GOP by President Bush. In the race for nonvoting delegate to the House, vacated by Democrat Walter E. Fauntroy in his unsuccessful bid for the mayoral nomination, former Carter administration official Eleanor Holmes Norton (D) faces former Reagan administration official Harry M. Singleton (R), who acknowledged prior marijuana use. Party-line voting makes Norton the favorite despite the two-month furor over her failure to file local income taxes for the past eight years. DELAWARE

His ill-starred 1988 presidential race apparently has not damaged Sen. Joseph R. Biden Jr. (D) a bit at home. Deputy state Attorney General M. Jane Brady (R), his novice challenger, has tried to revive some of the plagiarism charges that undermined his White House bid, but Biden is cruising to a fourth term. MAINE

Down East voters love having two nationally known senators and this year it's Republican Sen. William S. Cohen's turn to receive their accolades and a third term. State Rep. Neil Rolde (D) used the campaign to promote national health care rather than to attack Cohen -- probably a smart choice.

But those same voters have agonized about the choice between Gov. John R. "Jock" McKernan Jr. (R), who is seeking a second term, and former governor Joseph E. Brennan (D), who decided to come home after four years in the House to reclaim his old job. Brennan took the early lead, exploiting public unhappiness with the recurrent budget crises in Augusta brought on by the regional economic slump. But when Brennan got caught in the national budget bind, McKernan recovered. Some of Brennan's negative TV spots backfired, and polls show McKernan gaining the lead.

In Brennan's House district (formerly held by McKernan), state Sen. Thomas H. Andrews (D) has been transformed from distinct underdog to the favorite over former representative David F. Emery (R). Emery flip-flopped to an abortions-rights stance and still carries scars from his 1982 challenge to Maine's other venerated senator, Majority Leader George J. Mitchell (D). MARYLAND

Gov. William Donald Schaefer (D) is headed for an easy second-term victory over William S. Shepard (R), the Potomac diplomat and political novice who picked his wife, Lois, as his running mate for lieutenant governor.

Rep. Roy Dyson (D) has been hit with office scandals, financial ties to defense contractors and the revelation that, despite his hawkish views, he sat out the Vietnam War as a conscientious objector. His opponent, high school teacher and Vietnam veteran Wayne T. Gilchrest (R), lost by only 1,540 votes last time, but Dyson looked strong against Democratic primary opposition and is putting up a stiff battle again. MASSACHUSETTS

After setting off more verbal fireworks than any candidate north of Texan Clayton Williams, Boston University president (on leave) John R. Silber (D) seemed poised to win the governorship against William F. Weld (R). Silber made himself the loudest voice in the mass protest against the legacy of retiring Gov. Michael S. Dukakis (D), yet appealed to traditional Democrats by promising his own big preschool and jobs programs. Weld, who tied his candidacy to a tax-limit initiative that once seemed far more popular than it does now, is within upset range, and late polls showed he was having success wooing the anti-Silber liberals into a Republican coalition.

Senate challenger Jim Rappaport (R), 34, spending millions of his family's development money, tried to make voters think Sen. John F. Kerry (D), 46, was a Dukakis clone, but Kerry showed himself not only taller but tougher than Dukakis and stopped the game while he still had a lead. After early shakiness in several cases, all the House incumbents seem likely to survive, albeit with some shaved margins. NEW HAMPSHIRE

With one notable exception, everything is in order in this Republican bastion. Despite the economic slump, first-term Gov. Judd Gregg (R) is holding on against former Democratic state chairman J. Joseph Grandmaison. Grandmaison barely beat a more conservative Democrat in the primary and Gregg is attacking him as a high-tax liberal.

Rep. Robert C. Smith (R) should take over the seat of retiring Sen. Gordon J. Humphrey (R). His rival, former one-term senator John A. Durkin (D), has reminded people of his penchant for controversy with loose-lipped talk about "Jap" lobbyists' money influencing Smith.

The possible upset lies in Smith's old House district, where Manchester lawyer Joseph F. Keefe (D) has proved to be an effective campaigner against wealthy hotel owner Bill Zeliff (R). Zeliff survived a close and contentious Republican primary mainly through the public intervention of White House Chief of Staff (and former New Hampshire governor) John H. Sununu. He has repudiated the budget deal Sununu engineered on behalf of President Bush, but has not solidified Republican support in a district Democrats held from 1974 to 1984. NEW JERSEY

With overwhelming name recognition, high approval scores and a $12 million campaign treasury, Sen. Bill Bradley (D) could normally name his own margin over former public utilities commissioner Christine Todd (R), his challenger for a third term. But public distaste for the tax increases pushed through this year by new Gov. James J. Florio (D) may fuel some protest votes.

The Florio factor is stronger in the race for the House seat he vacated in January to become governor. Robert E. Andrews (D), the Camden County freehold director backed by Florio's organization, is getting a stiff challenge from Daniel J. Mangini (R), a Gloucester County freeholder who has a ready-made issue, but Andrews holds the lead.

In the House seat vacated by the retirement of Rep. Jim Courter (R), who lost the governorship to Florio, state Sen. Dick Zimmer (R) is a clear favorite over self-financed liberal philanthropist Marguerite Chandler (D). NEW YORK

How can a state this big and dynamic have an election so absurd? Gov. Mario M. Cuomo (D) is confident enough of winning a third term that he spent part of Columbus Day campaigning in Illinois. He has reason: Republican financier Pierre A. Rinfret, an unknown and a last-minute choice as the candidate, has blasted the party that nominated him, threatened to end his campaign and done everything but cause Cuomo a moment's concern. One poll has him barely edging Conservative Party nominee Herbert London. Not one of the 34 House seats seems likely to change hands. PENNSYLVANIA

It took Gov. Robert P. Casey Jr. (D) many tries to win his job, but now that he's got it he's not giving it up. His initiatives on auto insurance, jobs, schools and the environment have solidified support, and the one-note campaign of his under-funded challenger, Auditor General Barbara Hafer (R), who is flogging him for signing two restrictive antiabortion measures, has failed to dent his commanding lead. RHODE ISLAND

Gov. Edward D. DiPrete (R) is being buried in the collapse of the regional economy and complaints about his wavering leadership. The near-certain winner is wealthy businessman Bruce Sundlun (D), 71, who lost to DiPrete twice before but survived a tough Democratic primary to win a third chance in a year when Democratic victory was nearly certain.

To the surprise of many outsiders, Rep. Claudine Schneider (R), 43, apparently has gotten nowhere in her efforts to dislodge five-term Sen. Claiborne Pell (D), 71. Both are popular, but the affection for Pell, combined with the prestige of his post as Foreign Relations Committee chairman, is so deep that voters have been telling Schneider they wish she had waited. Late polls show her at least 20 points behind.

Democrats are well-positioned to take over the House seat Schneider held for 10 years. Trudy Coxe (R), an environmental activist, was in a close race against state Sen. John F. Reed (D), a longtime critic of DiPrete, but disclosure that her husband had used state computers to aid her campaign proved a major embarrassment. In the other House district, freshman Rep. Ronald K. Machtley (R), who benefited from the S&L taint of incumbent Fernand J. St Germain (D) in 1988, has done a textbook job of entrenching himself against the challenge of campaign consultant Scott Wolf (D), who almost beat St Germain in the 1988 primary. VERMONT

Gov. Madeleine M. Kunin (D) is the third of the New England governors chased into retirement by the region's severe recession, and her successor is likely to be her predecessor, former governor Richard Snelling (R). Snelling saw much of his early lead melt under an assault on his environmental and fiscal record from former state senator Peter Welch (D), but he appears to be riding his reputation as a tough manager toward a fairly comfortable victory.

No such comfort awaits freshman Rep. Peter Smith (R), who gained more national publicity than local support by disagreeing strongly with Bush administration policies while introducing the president at a recent Vermont fund-raiser. Independent Bernie Sanders, the socialist former mayor of Burlington and classic anti-establishment outsider, is leading Smith in private and public polls. He profited from a backlash to a Smith ad attempting to link Sanders to Fidel Castro. The Democrats have only a token candidate in the race. Sanders has said he will seek admission to the House Democratic Caucus if he wins. WEST VIRGINIA

Sen. John D. Rockefeller IV (D) has not come close to spending the $12 million of personal funds he expended in winning his Senate seat six years ago -- and hasn't had to in this race. John Yoder (R), a Harpers Ferry lawyer, is trying to play off resentment of Rockefeller's financial advantage, an ever-present factor in his races, but the contest is completely one-sided.

The only serious House race involves Rep. Harley O. Staggers Jr. (D), whose father was a longtime House member. Young Staggers faces Oliver Luck (R), a Huntington lawyer and, more importantly, a former West Virginia University quarterback who went on to play for the Houston Oilers. Republicans have carried this district, but the Staggers name has been solid electoral insurance for two generations.