A majority of Americans oppose the $98.3 billion tax increase that the House is scheduled to vote on today, according to a Washington Post-ABC News poll.

In interviews nationwide Tuesday evening, 24 hours after President Reagan's nationally televised speech in behalf of the bill, 54 percent said they were against it, while 38 percent said they favored it.

Rank-and-file Republicans whose party's trademark has been opposition to increased taxes support the president and the bill by 2 to 1. Democrats expressed opposition by more than 3 to 1; independents were more evenly divided, opposing the bill 5 to 4.

Nationally, the only region to show support was the Far West, where a plurality of 49 to 42 percent favored the bill. The strongest opposition, at about 2 to 1, came from the Midwest.

The poll, conducted by telephone, shows the public to be skeptical about whether the bill, if enacted, would achieve the results Reagan has predicted.

In his televised address, for example, Reagan said the combination of tax increases and spending reductions in prospect would reduce budget deficits $380 billion over three years. Only three in 10 of those interviewed by The Post and ABC News feel the bill would lower the deficit substantially, however. Six in 10 feel it would affect the deficit either little or not at all.

In addition, relatively few citizens accept the Reagan contention that the bill "could be called the greatest tax reform in history" rather than the greatest peacetime tax increase. Fewer than a third say the bill would make the federal tax system fairer; more than half say it would not.

Reagan has termed the bill 80 percent reform and 20 percent tax increase. The general reaction to that is uncertainty or disagreement.

Question: "Would you say the bill is more tax reform or more a tax increase, or don't you know enough to have an opinion on that?"

Response: more tax reform, 14 percent; more tax increase, 32 percent; mixture of both, 3 percent; don't know enough, 51 percent.

Since last winter, polls have found strong majorities believing the president's recovery program has hurt rather than helped the economy. That feeling persists, with only 32 percent saying that Reagan's "overall economic program is working" and 62 percent saying it is not.

A majority of 55 percent say they disapprove of Reagan's handling of the economy, while 40 percent say they approve. With minor shifts, that sentiment has remained constant since February, according to Post-ABC News polls.

The same holds for views as to whether the economy is getting better, getting worse or staying the same. Fewer than a fifth of the people feels the economy is improving, half say it continues to worsen, and the rest do not see any change.

More significant politically, perhaps, is the new poll's finding that many Americans see Reagan's call for a tax increase as a major flip-flop despite his statement Monday that the bill "absolutely does not represent any reversal of policy or philosophy on the part of this administration, or this president."

Question: "Reagan cut income taxes last year. Now he is calling for new taxes. Do you think this means Reagan has lost faith in his economic program of spending cuts and tax cuts or not?"

Response: Reagan has lost faith, 48 percent; Reagan has not lost faith, 41 percent; no opinion, 11 percent.

And in a related area, the tax bill, with its sponsors' emphasis on fairness, has not altered the perception that Reagan is a rich man's president.

In the 10 Post-ABC News polls since the president's first days in office, citizens have been asked whether Reagan "cares more about serving poor and lower income people, middle income people, upper income people . . . " or whether he "cares equally about serving all people."

In Tuesday's poll, which consisted of interviews with 913 people, 55 percent said Reagan cares more about serving upper income people, as high a proportion as have held that view in any of the 10 polls. Only 29 percent said he cares equally about serving all people, the lowest rating in that regard in any of the surveys.