Forty-eight hours before the polls open, the midterm campaign of 1978 seems likely to produce a "nothing" election. Democrats appear capable of blocking significant Republican inroads into their dominance of national and state government, but the views of winning candidates indicate that the slow drift toward a more comprehensive domestic policy is likely to continue.

A final, state-by-state survey of election prospects, beginning on Page D4, shows that prospects in a dozen senatorial and gubernatorial races have changed dramatically in the past month.

In a period of extraordinary economic uncertainty, the political climate in some states has been as unstable as the stock market.

But on balance, the party alignments in the Senate, the House and the state capitals seem unlikely to be only slightly less Democratic than they are today.

Reports from Washington Post correspondents on the campaign trail and local political reporters in all 50 states agree on one point:

"Negative campaigning" against opponents' alleged shortcomings has changed more races than any positive appeal to party loyalty, program or personality.

Interviews with half a dozen private pollsters and the campaign strategists in both parties' headquarters establish a second general point:

No one is likely to be able to claim any clear mandate from the election returns.

The independence of most Democratic congressional incumbents from White House control makes it impossible to consider the election a referendum on President Carter's midterm performance. And the backlash against Republican efforts to focus the voting solely on GOP proposals for sweeping tax cuts denies the opposition party its hoped for head start on the 1980 campaign.

One final "negative" overhangs all predictions about Tuesday's election - the likelihood that the vast majority of eligible Americans will stay home. Pollsters say the turnout could fall from the 36.6 percent in the last midterm election of 1974 to less than 33 percent - a low not seen since the wartime election of 1942.

Since absenteeism is usually heaviest among-low-income and minority voters who tend to be Democrats, a number of close races could swing to the Republicans if the turnout is as low as many expect.

Republican strategists note that their candidates lost 28 House seats in 1976 by 2 percent or less - a deficit that could easily be wiped out simply by the change in the political composition of an 1978 electorate significantly smaller than the 54 percent of eligibles who voted in 1976.

White House pollster Patrick Caddell warned Carter in a memo on the turnout question last week that while "this undefined election may conclude with the basically good showing expected for the Democrats . . . there are enough disturbing signs to suggest the possibility of a different outcome, with more serious losses than anticipated."

But even if Caddell's fears materialize, the election is unlikely to give Republicans the gains they hoped for when they launched their unprecedently expensive and well-staffed midterm election drive.

That is particularly the case in the gubernatorial and state legislative battles that measure grassroots party strength. Odds now favor Republicans making a net addition of only four or five states to the dozen governorships they currently control. In major states, Republicans have improved their chances for takeovers in Pennsylvania, Massachusetts and Wisconsin, and have marginally strengthened prospects for holding on in Illinois, Michigan and Ohio. But Democrats now seem almost certain to govern California, New York, Texas and Florida - all of which at one point seemed possible for Republicans to win.

In the Senate, where Democrats have a 62-to-38 advantage, the final field reports suggest a literal standoff.

Democrats are favored to take over seats vacated by Republicans in New Jersey, Nebraska and Oklahoma, but Republicans are favored in Democratic vacancies in Mississippi, South Dakota and the Minnesota battle between David L. Durenberger (R) and Robert E. Short (D).

Each party has six seats in serious jeopardy. The Republicans' are Sens. Edward W. Brooke (Mass.), John G. Tower (Tex.), Charles H. Percy (I11.) and Robert P. Griffin (Mich.), as well as the vacant seats in Kansas and Virginia.

Democrats must worry about Sens. William D. Hathaway (Maine), [WORD ILLEGIBLE] Randolph (W.Va.) and Floyd Haskell (Colo.), as well as vacant seats in Alabama and Montana.

Only in House races have Republicans raised their sights slightly on the basis of the most recent field reports.

There are now about 40 Democratic held seats where Republicans have a realistic possibility of winning, and there are reasonable odds that hlaf those may come through. But two dozen Republican seats are equally in trouble.

A down-the-middle split might yield the Republicans a net gain of 10 House seats - hardly enough to change the power balance represented by the current House lineup of 285 Democrats and 146 Republicans, with three vacancies.

The GOP House gain could easily be larger if voter turnout falls to the levels now predicted. But an offsetting factor is that Democratic state tickets appear strong in several of the states where Republicans have possibilities of multiple-seat pickups: New Jersey, New York, Florida, Texas and California.

In California, Gov. Edmund G (Jerry) Brown Jr. (D) appears headed for a landslide, and the latest New York polls show Gov. Hugh L. Carey (D) pulling away from his challenger.

Other states where Democrats are now favored to retain the governor ship include: Alabama, Arizona, Arkansas, Colorado, Connecticut, Florida, Georgia, Hawaii, Idaho, Maryland, Minnesota, Oklahoma, Rhode Island, Texas and Wyoming.

Republicans are favored to stay in power in Alaska, Illinois, Iowa, Kansas, Michigan, New Hampshire and Vermont.

Democrats are favored to take over in South Carolina and replace the retiring independent governor of Maine. Switches from Democrats to Republicans are likely in Nebraska, Nevada and Oregon - although none of the three is a certainty.

What is left of the once-high hopes Republicans had in the gubernatorial battles lies in the fact that six of the seven closest races are in states now held by the Democrats. Democratic control is in jeopardy in Masshachusetts, New Mexico, Pennsylvania, South Dakota, Tennessee and Wisconsin while Gov. James A. Rhodes (R) is in close fight for reelection in Ohio.

Legislative races are tied closely to the gubernatorial battles in most states. Thus the decline in GOP prospects for additional governorships also put in jeopardy their long-term goal of a significant increase in legislative strength before redistricting begins after the 1980 census. Republican National Chairman Bill Brock says he hopes to gain four to six governors and 200 legislators this year - a target that may be hard to meet.

Another minority that has looked with anxiety on this election are the women members of Congress. Both women senators and three women House members are retiring and none will have female replacements.

However, none of the other women House members appears likely to be defeated and there is a prospect of women being elected in districts in Maine and Maryland, with lesser possibilities in half a dozen other states.

In Kansas, Nancy Kassebaum (R) has battled back up to an even chance in her Senate race with ex-representative Bill Roy (D). And a few observers think Jane Eskind (D) may upset Senate Minority Leader Howard H. Baker Jr. (R-Tenn.), although more think she will have to be content with reducing his margin of victory.

The Kassebaum-Roy battle is typical of the dozen races that have oscillated wildly on the polling charts since Labor Day. She was the favorite after winning the Republican primary to succeed retiring Sen. James B. Pearson (R-Kan.), then fell behind, and is now even and rising.

Others who have ridden that rollercoaster include Colorado Gov. Richard D. Lamm (D), Pennsylvania gubernatorial rivals Pete Flaherty (D) and Richard L. Thornburgh (R), and the Massachusetts gubernatorial opponents, Edward J. King (D) and Francis W. Hatch Jr. (R).

All of them have known the dizzying sensation of being ahead, then behind, then maybe ahead again.

That is tough on the nerves, but not as bad as on those who thought they were far in front and have seen their leads erode to the point of jeopardy. That happened most dramatically to five Senate candidates: Sen. Charles H. Percy (R) in Illinois, Rep. Max Baucus (D) Montana, State Sen. Donald Stewart (D) in Alabama, and Bob Short (D) and Rudy Boschwitz (R) in Minnesota's two races.

There are some strange patterns in the campaign. Despite their generally modest prospects, Republicans may be on the verge of electing their first senator from Mississippi, where Rep-Thad Cochran (R) is favored, and perhaps from Alabama, where ex-representative James D. Martin (R) is challenging Stewart. But for the first time in history, Republican Nebraska is likely to be represented by two Democrats in the Senate when Gov. J. James Exon joins Sen. Edward Zorinsky.

Another oddity: Two Republican governors - Jay S. Hammond of Alaska and Meldrim Thomson Jr. of New Hampshire - apparently have improved chances of reelection because the former Republican governors they defeated in their primaries have now entered the general election as independents. The activities of ex-governors Walter J. Hickel in Alaska and Wesley Powell in New Hampshire are believed to be scattering the incumbents opposition and thus reducing the likelihood of Democratic victories.

Aside from such footnotes to the political almanac, the main significance of 1978 seems likely to lie less in who wins than in what has emerged as the dominant tone in the vast majority of campaigns.

That is the critical attitude toward taxes, government spending, bureaucracy and regulations, voiced by Democrats as well as Republicans.

With a boost from the tax-and spending-limitation initiatives on the ballots in 16 states Tuesday, the move toward slimmed-down government and reduced taxes is likely to get a push, no matter who is elected.

Whether those promises will be translated into a goverment policy, however, will be judged in 1980 - an election which most will say is blessedly still two years away.