It's time again.

Illinois broke the ice in March with its primary but from Tuesday on, when North Carolina and Indiana vote, until Florida's Oct. 10 runoff completes the process there is hardly a respite in the election schedule.

These primaries are, of course, the warm-ups for the Nov. 7 general election, when 34 Senate Seats, all 435 House Seats, 36 governorships and a host of lesser offices will be filled.

Active participants in the campaigning over the next six months will be Jimmy Carter and Waleter F. Mondale, for whom the first mid-term election of their administraion constitutes - to some degree - a vote of confidence or no confidence.

But they will be no busier than the dozen big-name Republicans - including 1976 rivals Gerald Ford and Ronald Reagan - who will use this mid-term campaign as a way of building political IOUs for a possible 1980 presidential nomination bid.

At this early stage of the season, the expection of leaders in both parties is the Republicans will make modest to moderate gains. The gains could become major if the economy, which now looms as the major national issue, spins into more sever inflation or suddenly slumps into recession before election day.

But, as often is the case in an off-year election, local issues and the strengths of individual candidates probably will be more important than any national trend in determining the outcome.

The sharp decline in Carter's political fortunes has not - so far as polls can measure - rubbed off on other Democrats.

District-by-district surveys bear out the message of the national polls that, generally speaking, congressional incumbents are in good shape with their constituents.

For the Democrats, with their big majorities in both House and Senate, that is good news. Few are as optimistic as House Speaker Thomas P. (Tip) O'Neill Jr (D-Mass.), who went on record as saying his party would lose fewer than five seats in the House.

But there is a rough consensus that a loss of 15 to 20 seats, which would not be regarded as a serious setback to the Democrat's 288-147 lead, probably represents the current outer limit of Democratic risk.

In the Senate, where Democrats have an edge of 62 to 38, the early outlook is for a near-standoff. By the luck of the Senate rotation, Republicans are defending just as many seats this year as are the Democrats. Each party has 17 at stake, and each appears to have as many volnerable spots to defend. A half-dozen seats in each party could change hands.

The picture is quite different in the gubernatorial races, where the statistical and political odds look much better for a significant Republican gain. Of the 36 governorships up this year, Democrats hold 26 and Republicans have nine. The other is held by Maine's retiring independent, James B. Longley.

With targets ranging from such industrial states as Connecticut, New York and Pennsylvania to nine western states, the Republicans have more tages through their command of staffs, district offices, publicity and campaign funds.

In the past decade, more than 90 percent of the congressional incumbents on the general election ballot have been reelected. As a result, competition focuses heavily on the open seats, where incumbents are retiring or running for other offices.

Those seats will be more abundant than usual this year. Nine of the 34 Senate races have no incumbent running, and the list of "open seats" in the House has passed the 40 mark, with the total expected to rise as other states reach filing deadlines.

Most of the open seats are held by Democrats, and the Republcans' record in special elections in the past 15 months encourages their hopes that they can do well where there is no Democratic incumbent.

The GOP won four of six Democratic House vacancies since the last presidential election. With their well-nourished campaign treasury and the most intensive candidate recruitment in recent years, the Republicans are hopeful of scoring multiple-seat gains than their share of opportunities.

The general prosperity in state budgets - allowing many governors to reduce taxes rather than raise them this year - may be of help to the incumbents. In Congress, the incumbents have built up enormous advanin states like Texas, where six Democratic incumbents are retiring or running for other offices.

But politics is not as much a matter of numbers as of personalities, and the 1978 election has many colorful and important contests. Here are some that will draw attention:

Alabama - Gov. George C. Wallace has three Democratic challengers for the seat of retiring Sen. John Sparkman (D), while threee prominent Democrats, including Wallace's foe, ex-governor Albert Brewer, vie for the governorship.

Alaska - Bearded Gov. Jay S. Hamond (R) faces a rematch in the primary with ex-governor Walter J. Hickel (R).

Arkansas - A wholesales shuffle is in prospect as Gov. David Pryor (D) and Reps. Ray Thornton (D) and jim Guy Tucker (D) seek the nomination for a vacant Senate seat.

California - Gov. Edmund G. (Jerry) Brown Jr. (D), although slipping in the polls, has no serious primary opposition. Polls show Assemblyman Kenneth L. Maddy - a dark horse but the man many Democrats see as the biggest threat to Brown - moving up on the front-runners in the GOP primary field, Attorney General Evelle J. Younger and Ed Davis, former Los Angeles police chief.

Connecticut - Gov. Ella Grasso (D) has a nomination challenge from Lt. Gov. Robert L. Killian (D) and faces a serious GOP contender in the fall, probably Rep. Ronald L. Sarasin.

Illinois - Gov. James R. Thompson (R) is hoping to increase his presidential credentials in a reelection bid that may be bolstered by the presence on the ticker of Sen. Charles H. Percy (R).

Maine - Sen. William D. Hathaway (D) faces Rep. William S. Cohen (R) in a classic contest between two very popular vote-getters.

Minnesota - Both Senate seats and the governorship - all held by Democrats who inherited or were appointed to their jobs - are up for grabs and the state's downtrodden Republicans are challenged for all three.

Mississippi - The retirement of Sen. James O. Eastland (D) has drawn out the best vote-getters in both parties, and the independent candidacy of civil rights leader Charles Evers should make the fall contest a real race, too.

New Jersey - Four-term Sen. Clifford P. Case (R: has a conservative challenger in the primary and a possibly tough race from professional basketball player Bill Bradley (D) or manager-turned-candidate Richard Leone (D) in the fall.

New York - Gov. Hugh L. Carey (D) faces Assembly Minority Leader Perry B. Duryea (R) in a key fight whose outcome no one will guess.

North Carolina - Conservative spokesman sen. Jesse Helms (R) has drawn a big field of Democratic opponents and he may need the large campaign fund he has raised for the general election.

Ohio - Three-term Gov. James A. Rhodes (R) appears a strong bet to overcome a primary challenge and the autumn candidacy of ambitious Lt. Gov. Richard F. Celeste (D).

Oregon - The comback bid of Tom McCall (R) . a maverick ex-governor, is a serious threat to Gov. Robert Straub (D).

Pennsylvania - Both parties have spectacular primaries to choose a successor to Gov. Milton J. Shapp (D), whose scandal-stained administration is the main target of all contenders.

The players include on the Republican side, ousted U.S. attorney David Marston and former prosecutors Richard Thornburgh and Arlen Specter. The Democrats are former Pittsburgh mayor Pete Flaherty, former auditor Robert P. Casey and Lt. Gov. Ernest Kline, who is not shy in criticizing his former colleagues in the Shapp administration.

South Carolina - Sen. Strom Thurmond (R), 72, the best politician of the past generation, whichever ticket he was running on, faces Charles D. (Pug) Ravenel (D), 40, the best politician of the new generation, in what promises to be a close race.

Tennessee - Senate Minority Leader Howard H. Baker Jr. (R) has minimal opposition so far in a race that will be a stepping-stone for his presidential ambitious.

Texas - After several years of somnolence, Texas politics has awakened with a roar. Gov. Dolph Briscoe (D) has all the opposition he can handle in the primary from Attorney General John Hill (D), but the Republicans will mount another major challenge in the fall. Sen. John Tower (R), well-financed as usual, faces a strong opponent in the probable winner of the Democratic primary , Rep. Bob Krueger (D).

West Virginia - Sen. Jennings Randolph (D) faces his toughest test in years from Arch A. Moore (R), a former governor.