COMING OFF a better-than-expected 2-to-1 victory over her lieutenant governor, Robert K. Killian, in a bitter September Democratic primary, Gov. Ella T. Grasso (D), 58, has made herself a slight favorite for a second term. But she is still in a tough race with Rep. Ronald A. Sarasin (R), 43, the nominee of a resurgent Republican Party. A post-primary Hartford Courant poll gave Grasso a 47-43 percent lead, but with intraparty tensions negating the 200,000-vote Democratic registration lead, Sarasin is still a real threat.

Former House Speaker William R. Ratchford is a slight favorite to recapture Sarasin's House seat for the Democrats, but state Sen. George C. Guiders (R) could benefit from Sarasin's coattails. Rep. Robert N. Giamo (D), chairman of the House Budge Committee, appears to be withstanding a second challenge from John G. Pucciano (R), who surprised everyone by coming withing 25,000 votes of an upset in 1976. DELAWARE

SEN. JOSEPH R. BIDEN JR. (D), 35, an early Carter supporter who is flexible enough to take a strong anti-busing stand and support the Kemp-Roth tax-cut proposal, is expected to have little trouble winning a second term against James H. Baxter Jr., 54, a farmer-businessman and GOP county chairman.

Equally safe is freshman Rep. Thomas B. Evans Jr. (R), who is opposed by Gary E. Hindes (D), a youthful unemployed reporter and legislative aide, who is sleeping in the back room of his headquarters to save rent money. MAINE

WITH INDEPENDENT Gov. James B. Longley retiring after one term at the height of his popularity, independents have entered - and are clouding - both the governor and Senate races.

In the former, Atty. Gen. Joseph E. Brennan (D), 43, appears to be leading House Minority Leader Linwood E. Plamer Jr. (R), 56, and the Rev. Herman C. (Buddy) Frankland, 43, the independent candidate.

In the Senate race, Sen. William D. Hathaway (D), 54, an upset winner six years ago over then-Sen. margaret Chase Smith (R), has been trailing in his bid for a second term against Rep. William S. Cohen (R), 37, who has rolled up record majorities in his three House races. The independent here is Hayes Gahagan, 30, a conservative supported by some GOP leaders.

Labor unions are striving to help Hathaway counter Cohen's campaign for blue-collar votes, and President Carter has scheduled a return trip to help save the seat. Some observers think Hathaway's low-key appeals are beginning to blunt Cohen's drive, but Cohen remains the favorite.

Secretary of State Markham L. Gartley (D) is given a slight edge on state Sen. Olympia J. Snowe (R), one of the best-regarded women candidates in the country, in the race for Cohen's House seat. MARYLAND

HARRY R. HUGHES (D), 51, the former state transportation secretary who upset acting Gov. Blair Lee III, (D), in the primary, is the favorite in this normally Democratic state. His opponent is ex-Sen. J. Glenn Beall Jr. (R), 51. Beall faces a problem in exploiting the scandals in the previous Democratic administration against a Democratic nominee identified by the public as a sharp critic of past practices.

The closest House race is the challenge to freshman Rep. Newton I. Steers Jr. (R) by Michael D. Barnes (D), former state public service commissioner. Most observers give Steers the edge. MASSACHUSETTS

BOTH PARTIES have had trouble finding any semblance of internal unity after the September gubernatorial primaries in which conservative Edward J. King (D), 53, upset Gov. Michael S. Dukakis (D), and liberal Francis W. Hatch Jr. (R), 53, turned back conservative Edward F. King (R). King, former executive director of the Massachusetts Port Authority, has rejected suggestions from other Democrats that he soften his antitax rhetoric. Dukakis has withheld his support and many other liberal Democrats are openly pro-Hatch. Hatch, minority leader of the state House of Representatives, has problems with conservative Republicans. He trailed King by 12 to 25 points in one public and two private polls after the primary, but this race has not yet jelled enough for anyone to be confident of the outcome.

Sen. Edward W. Brooke (R), 59, who withstood a serious conservative challenge to renomination, still has a major hurdle to winning a third term. Rep. Paul E. Tsongas (D), 37, campaigned skillfully in winning the primary, and Brooke's personal and financial problems, stemming from a messy divorce, cloud his chances. The Senator is a slight favorite, but not home free.

Close races are expected in the districts vacated by Tsongas and retiring Rep. Michael J. Harrington (D), but the edge goes to Democrats in what may be close races. NEW HAMPSHIRE

CONTRARY to earlier expectations, the governor's race appears to be tighter that the Senate contest.

Gov. Meldrim Thomson Jr. (R) 66, a leader of the national conservative movement may be hard pressed to win an unprecedented fourth term. In the past, Thomson has won on his opposition to broad-based taxes, but he is involved now in a controversy over a utilities surcharge for construction costs of the Seabrook nuclear plant. He is being attacked on this issue by former state Rep. Hugh J. Gallen (D), 54. Ironically, Thomson may be helped by the decision of ex-Gov. Wesley Powell (R), 62, who won almost 40 percent of the GOP primary vote against him, to run as an independent in the general election. A New Hampshire poll showed Thomson leading Gallen by 12 points with Powell in the race, and by only 3 points in a theoretical two-way contest. But some Democrtas think Powell's share of the vote will erode as election day nears and that Gallen will make it a close contest.

Sen. Thomas J. McIntyre (D), 63, is a strong favorite for a third term over airline pilot Gordon Humphrey (R), 37, a novice candidate recruited by Thomson from Conservative Caucus ranks. No change is expected in the House. NEW JERSEY

THE LATEST Rutgers University poll shows basketball star Bill Bradley (D), 34, holds a 49-to-24 percent lead over Jeffrey Bell (R), 34, the former Ronald Reagan aide who upset Sen. Clifford P. Case (R) last June. Bell has continued to plug for the Kemp-Roth tax-cut bill, as he did in the primary, and has scored well in joint appearances with Bradley. But he has found no answer for the ex-New York Knick's star quality, and the gap he has to close would make a Bell victory even more of a surprise than his ouster of Case. Democrats count this as a near-certain Senate pickup.

However, there are serious Democratic worries about the reelection of Rep. Helen Meyer (D) and some misgivings about the chances of Rep. Edward J. Patten (D). NEW YORK

ON PAPER, Gov. Hugh L. Carey (D), 69, scarred by controversy over taxes, his death penalty veto and his personal style during his first term, has looked highly vulnerable. He won barely 50 percent of the primary vote against two opponents. But his opponent, Assembly Minority Leader Perry B. Duryea (R), 56, plagued by campaign problems that finally forced him to fire his manager, has had trouble exploiting Carey's liabilities. Republicans are cheered by a recent private poll showing Duryea more than 10 points ahead, and hope that a media campaign and the possible return of New Yokr City morning newspapers will help Duryea hold his lead. But Democrats think that Carey, who is the superior campaigner, may still pull it out.

New York is a major battleground for the House, with four open seats and several endangered incumbents. Republicans have even chances or better in the districts of retiring Democrats Otis G. Pike and James J. Delaney and are threatening to defeat incumbents Jerome A. Ambro and Ned Pattison. But Democrats have a good shot at the seats of retiring Republicans Bruce F. Caputo (the GOP candidate for lieutenant governor) and William F. Walsh. Overall, odds favor a one- or two-seat GOP gain. PENNSYLVANIA

SCANDALS in the administration of retiring Gov. Milton J. Shapp (D) made this a year of opportunity for the GOP, but Democrats are now favored to retain the governorship. Former Pittsburgh mayor Pete Flaherty (D), 53, has reinforced his longtime independent image by shunning any ties with Sharp and concentrating on his claim to have cut taxes and payrolls in Pittsburgh. Former federal prosecutor Richard L. Thornburgh (R), 45, has had trouble consolidating GOP support and broadening his campaign base since winning the primary with less than a third of the vote. But Thornburgh is well-financed for a closing TV drive and may cut a Flaherty margin which both parties now regard as almost insurmountable.

Rep. Joshua Eilberg (D), target of federal investigations, is probably trailing in his bid for reelection, but indicated Rep. Daniel J. Flood (D) has no election problem. Other Democrats in jeopardy are freshman Rep. Joseph S. Ammerman, hospitalized for many weeks from an auto injury, sophomore Rep. Robert W. Edgar and veteran Rep. William S. Moorhead, who has an unusually active opponent. But Democrats are expected to retain the seat of retiring Rep. John H. Dent (D) and take the seat of retiring Rep. Gary A. Myers (R). RHODE ISLAND

IT LOOKS like a Democratic sweep of the major races. Gov. J. Joseph Garrahy (D), 47, is favored for a second term over former U.S. attorney Lincoln C. Almond, 42, and former Providence mayor Joseph A. Doorley, 47, a Democrat running as an independent. Sen. Claiborne Pell (D), 59, should breeze to a fourth term over James G. Reynolds (R), 35, a bakery executive and political newcomer. Democrats are expected to hold both House seats. VERMONT

POLITICS has barely disturbed anyone's enjoyment of the foliage in Vermont this year. Republican incumbents were unopposed for renomination and fewer than 13,000 voted in the primary for their underdog Democratic challengers.

Gov. Richard A. Snelling (R), 51, who has managed to cut taxes in each of his first two years in office, is a strong favorite for a second term over state Rep. Edward Granai (D), 46, a business consultant and Presbyterian minister.

Rep. James M. Jeffords (R), a solar energy backer with strong labor support is opposed by S. Marie Dietz, a right-to-life activist who won the Democratic nomination over the choice of pary leaders. Jeffords seems safe for a third term. WEST VIRGINIA

SEN. JENNINGS RANDOLPH (D), 76, is seeking to extend a congressional career that began in 1932, but his opponent, ex-Gov. Arch A. Moore (R), 55, is the strongest Republican political figure in the state's recent history. Randolph, who broke with President Carter on both Panama and public works, has still received two presidential campaign visits, the most recent yesterday. Polls show the race a virtual tossup, but Moore has the edge as a campaigner and may rate a slight favorite.

No change is likely in the all-Democratic House delegation.