A SLOW-STARTING Reagan campaign and a strong push for Carter by Gov. Ella Grasso (D) have given Carter an opening in this state, which he lost by 71,000 votes in 1976 and lost to Kennedy in the primary. Anderson's strength has been high here (a mid-September University of Connecticut poll showed the three candidates virtually tied in the high 20s) and the question is whether Carter can peel off more of the Anderson vote than Bush, with his family roots here, can lure to Reagan.

Rep. Christopher Dodd (D) is favored over ex-New York Sen. James L. Buckley (R) for the seat of retiring Sen. Abraham A. Ribicoff (D). But Buckley has done well in their debates, and the margin could be shrinking.

Democrats expect to hold the Dodd seat with former state Rep. Samuel Gejdenson, but may have a harder time in the district of retiring Rep. Bob Giaimo; some of his backers are helping former state Sen. Lawrence DeNardis (R) against state Sen. Joseph Lieberman (D). Belaware (3)

CARTER HAD a 5-percent win here in 1976, but is running virtually even with Reagan in private polls in September. His problem is Anderson, whose 15 percent share is coming mainly from suburban Wilmington Democrats.

Gov. Pierre S. (Pete) du Pont (R), opposed by state House Minority Leader William J. Gordy (D), is far ahead, as is Rep. Thomas B. Evans Jr. (R), a national leader of the Reagan campaign. DISTRICT OF COLUMBIA (3)

CARTER LOST to Kennedy in the primary but will win easily in November. Reagan will have some votes west of Rock Creek Park, and Anderson will get some there and on Capitol Hill. Delegate Walter Fauntroy (D) has only token opposition from Bob Roehr (R). MAINE (4)

WHETHER IT was the appointment of Maine's Edmund S. Muskie as secretary of state or the weakness of Reagan is showing generally in a region that prefers moderate Republicans to hard-line conservatives, Maine -- which Carter lost by 4,041 votes last time -- is a possible win for him this year. A University of Maine poll for the Bangor Daily News in early September showed Carter 36.9, Reagan 35.2, Anderson 17. Without anderson, it said, Carter would lead by 10 points. More recent private polls confirm Carter's narrow lead, which is likely to grow if Anderson fades. There is no Senate race and the two Republican House members seem safe. MARYLAND (10)

A COMFORTABLE WIN for Carter last time, it leans -- perhaps a bit less securely -- in his direction again. Turnout problems in Baltimore and Prince George's County and a significant Anderson vote in Montgomery County could hurt Carter. But Reagan's brand of conservation has not done well in this state.

Sen. Charles McC. Mathias, Jr. (R), a moderate seeking a third term, is keeping his distance from Reagan and is far ahead of state Sen. Edward T. Conroy (D).

Ex-Rep. Newton Steers (R) is mounting an aggressive contest in his rematch with his 1978 conqueror, Rep. Michael D. Barnes (D), in Montgomery County, and the race is judged a tossup. Veteran Rep. Clarence D. Long (D) has an unusually strong challenge from former Federal Maritime Commission Chairman Helen Delitch Bentley (R), but is favored. Rep. Robert E. Bauman (R) was strongly favored for reelection from the Eastern Shore, but publicity last week about his sodomy case has thrown his contest with Del. Roy Dyson (D) into doubt. MASSACHUSETTS (14)

A STUBBORN AND SIGNIFICANT Anderson vote has kept Massachusetts from the Carter column, but it seems to be headed there. The Becker Poll released Oct. 1 had a three-way dead heat: Reagan, 27; Carter, 26; Anderson, 24. A private poll taken at the same time had Carter narrowly ahead. But with Kennedy and his organization leading active support to Carter while Anderson depends largely on student volunteers and Reagan leans on a virtually nonexistent Republican Party, the state is a likely Carter win.

The top House race pits freshman Nicholas Mavroules (D) against attorney Thomas H. Trimarco (R) in a district Republicans last held 12 years ago. State Rep. Barney Frank (D) is almost certain to succeed retiring Rep. Robert F. Drinan (D) and match his liberal record. NEW HAMPSHIRE (4)

TICKET-SPLITTING VOTERS will love New Hampshire this year. Reagan is a strong favorite, with a mid-September University of New Hampshire poll showing him with 45 percent, Carter 20, Anderson 18. But the same poll showed Gov. Hugh Gallen (D) leading ex-Gov. Meldrim Thomson Jr. (R), an outspoken conservative, 51 to 36, in a rematch of the 1978 contest. Gallen, an early Carter backer, is favored for a second term.

Sen. John A. Durkin (D), however, faces a stiff challenge in his reelection bid. The poll showed him leading former state Attorney General Warren Rudman (R), 42 to 33, but Rudman -- a moderate who came through a primary field crowded with conservatives -- is certain to close the gap as his name-recognition grows.

The retirement of veteran Rep. James C. Cleveland (R) has given Democrats an opportunity, and their candidate, Nashua Mayor Maurice L. Arel, has a good vote base. But GOP candidate Judd Gregg, a member of the executive council and son of former Gov. Hugh Gregg (R), has a well-known name and may rate the edge. NEW JERSEY (17)

EVEN MORE THAN most states, New Jersey is having a hard time deciding which candidate it dislikes least. An Eagleton poll in late September gave Reagan a 1-point lead among all voters and 5 points among likely voters, with Anderson just over 20 percent. A slight majority of Anderson's voters named Reagan as their second choice, but negative feelings toward both major-party candidates predominated in a state that is still some time away from casting its lot with either side.

There is no Senate race, but Republicans have four House seats in their sights and will be disappointed if they do not win more than one. The threatened Democratic incumbents are Andrew Maguire and James J. Howard, who have capable women opponents, and Frank Thompson Jr., who is being helped by Kennedy and organized labor to withstand the effect of his pending Abscam trial. There may also be a close race between state Sen. Bernard J. Dwyer (D) and insurance executive William J. O'Sullivan Jr. (R) for the seat vacated by Rep. Edward J. Patten (D). NEW YORK (41)

THE EMPIRE STATE, with much fussing and fumbling, appears to be moving into the Carter column again. Private polls confirm a Newsday-Gannett News Service Poll taken two weeks ago showing Carter with 35, Reagan 29, Anderson 15. Many among the 19 percent undecided are Jewish voters, who have been moving toward Carter as Anderson's fortunes have declined. The poll showed Carter outdrawing Reagan and Anderson combined among Jewish voters.

Rep. Elizabeth Holtzman (D) of Brooklyn has emerged as the favorite for the State since conservative Alfonse D'Amato, a Hempstead supervisor, upset Jacob Javits in the GOP primary. Newsday and the New York Daily News polls both put Javits, who is on the Liberal line, in third, fueling speculation he might withdraw. But Holtzman is favored in either a two-way or three-way race.

In House contests, the swing could be anywhere from four seats for the Republicans to two for the Democrats. The most seriously challenged incumbents include Jerome Ambro (D), John M. Murphy (D), who is awaiting trial on Abscam charges, Leo C. Zeferetti (D) and Matthew F. McHugh (D). Democrats have virtually conceded the seat of retiring Rep. James M. Hanley (D) to George Wortley (R), a newspaper publisher. Democrats are running tested women politicians for two Republican open seats, vacated by Reps. John Wydler and Robert C. McEwen. But the women, former State Sen. Karen Burstein and former Lt. Gov. Mary Anne Krupsak, are underdogs to Assemblymen Raymond McGrath (R) and David O'B. Martin (R). PENNSYLVANIA (27)

CARTER WON IT in 1976, but the most recent poll, taken by Gallup for the Pittsburgh Post Gazette last week, shows Reagan ahead, 38 to 34 percent among all voters, and 40 to 33 among the most likely voters, with Anderson at 16 in both measures. Carter is strong in western Pennsylvania, but has trouble in the hard-coal region; a low turnout in Philadelphia could hurt his margin. Reagan gained ticket-splitters leaving Anderson in the latest polls, but is still shaky in the suburbs.

In the race for the seat of retiring Sen. Richard S. Schweiker (R), the same poll shows former Pittsburgh mayor Pete Flaherty (D) leading former Philadelphia district attorney Arlen Spector (R), 49 to 41 among all voters and 48 to 43 among the likely voters. But Flaherty has much less money to spend and a reputation for late fadeouts, so the outcome is in doubt.

Republicans are looking for House gains. In Philadelphia, Michael (Ozzie) Myers, convicted in the Abscam scandal and ousted from the House Thursday, is expected to lose his seat to Thomas M. Foglietta, an independent who will probably caucus with the Democrats. Raymond F. Lederer (D), a second Abscam figure, had his trial postponed to January and is expected to win.

Republicans think they have the right candidates this year against Reps. Robert W. Edgar and Peter H. Kostmayer, two young Democrats who hold formerly Republican seats in the Philadelphia suburbs, but must worry about two of their own incumbents, Reps. Don Ritter and Marc L. Marks. Pittsburgh city councilman William J. Coyne (D) is favored over engineer Stan Thomas (R) for the seat of retiring Rep. William S. Moorhead (D). RHODE ISLAND (4)

THREE LATE-September polls gave Carter a 7-to-9-point edge in this traditionally Democratic state, and last week's WJAR-TV's 1,000-voter study had it Carter 41, Reagan 24, Anderson 17. Carter was trounced here by Kennedy in the primary but should hold it in November.

Gov. J. Joseph Garrahy (D) is favored for reelection to a third term over Providence Mayor Vince A. Cianci (R). Both skilled campaigners, they are debating the state's economy. Rep. Edward P. Beard (D) is in a close rematch with Claudine Schneider (R), a former television talk show hostess, who won 48 percent of the vote two years ago and has picked up more financial and organizational backing for a race the GOP has targeted nationally. VERMONT (3)

MOST VERMONT POLITICIANS assume that Republican habits make Reagan a clear favorite, but a series of private polls show Carter within a few points -- with one-third of the vote going to Anderson or undecided. Tradition gives Reagan a narrow edge.

Gov. Richard Snelling (R), seeking to become the first Republican in this century to win a third term, faces an old rival, Attorney General M. Jerome Diamond (D), a populist who contends that Snelling's businesslike administration has hurt social programs. Despite the presence of a conservative independent, Daniel Woodward, Snelling is expected to win.

Sen. Patrick Leahy (D), who became the first popularly elected Democratic senator in Vermont history in 1974 by only 4,400 votes, faces a hard reelection fight against Snelling's former banking and insurance commissioner, Stewart Ledbetter (R). Ledbetter, a moderate, gained momentum from his self-financed, come-from behind Sept. 9 primary victory, and Democrats think the favored Leahy will have to work hard to preserve his lead in the closing weeks of the campaign. WEST VIRGINIA (6)

AFTER A BETWEEN-CONVENTIONS slump, Carter has moved ahead of Reagan in two Charleston newspaper polls, by margins of 7 to 12 percent. A reversal of the historic pattern in normally Democratic West Virginia would be surprising.

Gov. John D. (Jay) Rockefeller IV (D) is spending several million dollars, buying TV and billboards even in neighboring states, to defeat ex-Gov. Arch A. Moore Jr. (R), who bested him for the job in 1972. Moore is fighting back with ridicule ("Make him spend it all, Arch," the bumper stickers read), but the polls show Rockefeller holding a steady 15-point lead.

Democrat Pat Hamilton is a slight favorite over Republican Cleve Benedict to succeed retiring Rep. Harley O. Staggers (D), and Rep. John G. Hutchinson (D) is expected to repeat his June special election victory over Mick Staton (R), despite unfavorable publicity in his first months on the job.