Americans disagree with President Reagan that they are better off than before he took office and are strongly supporting Democratic candidates in the Nov. 2 elections, in part because they see Republican economic programs as more menacing to the nation than Democratic alternatives, according to a new Washington Post-ABC News poll.

By almost 2 to 1, voters feel there is a greater danger in Republicans going too far in helping the rich and cutting needed government services than in Democrats going too far in keeping costly, wasteful and out-of-date services. This perception of the Democrats as the lesser of two evils, along with strong majority belief that President Reagan's programs are not working, continues to give the Democrats a 60 to 40 percent lead among likely voters in the congressional elections less than three weeks away.

The poll makes no attempt to convert that sizable overall lead into the number of seats the Democrats may gain in the House. Political leaders and analysts working with similar figures have estimated such a gain from eight to 40 seats.

Despite their strong leaning toward Democratic candidates, however, citizens regard the Democrats as only marginally better than the Republicans on a number of key issues. For example, asked which party could do "a better job in coping with the main problems the nation faces," 44 percent of those interviewed selected the Democrats and 38 percent chose the Republicans, with the rest offering no opinion or stating that neither party can do much of a job.

Similarly, despite widespread concern over Reagan's economic program, only 36 percent said that the Democrats in Congress "have been offering better plans than Reagan." Twenty-nine percent say the Democrats' plans are worse than Reagan's, and 4 percent say the Democrats have no plan at all. The remaining 31 percent express no opinion or say they see no difference in the merits of what the Democrats and Reagan are proposing.

While enthusiasm for them may be only lukewarm, Democratic candidates appear to be benefitting greatly from widespread concern that the Reagan administration has failed to improve the economy. That conclusion arises from poll findings such as these:

* By an almost 2-to-1 majority, 61 percent to 33 percent, the public rejects the recent assertion by Reagan that "people are better off today" than when he took office in January, 1981.

* Fifty-seven percent of those interviewed said "things in this country have gotten pretty seriously off on the wrong track;" only 35 percent feel things "are generally going in the right direction" -- a measure that White House political strategists themselves say is a vital one.

* Sixty percent of those interviewed said they disapprove of the way Reagan is dealing with "the financial problems of the Social Security system;" 26 percent say they approve.

* Sixty-nine percent said the Reagan Administration should do more to help the poor. Only 23 percent said the Administration is doing enough or too much to benefit the poor.

Reagan has pointed to a decrease in the inflation rate as a key accomplishment of his administration and an indication that better times are ahead, and Republican political advertising has focused on asking voters to "stay the course." But citizens appear to be taking a different view.

Question: "What's your impression of the prices you pay for things these days: Are prices going up a great deal, going up a fair amount, staying about the same, or going down?"

Response: Going up a great deal, 43 percent; going up a fair amount, 33 percent; staying the same, 21 percent; going down, 3 percent.

The Post-ABC poll conflicts to some degree with other surveys that say a majority of Americans feel the Reagan economic program will work in the long run despite some hard times along the way.

Asked how confident they are that "Reagan's economic program will improve the economy, 12 percent said they are very confident, 37 percent said they are fairly confident, 23 percent said they are not very confident and 25 percent said they are not confident at all.

And among those who expressed either a great deal or a fair amount of confidence, 9 in every 10 said it would take more than a year to produce any results.

Four Americans in 10 told Post-ABC News interviewers that the nation's biggest problem is unemployment, and one in every six workers polled across the country expressed concern that he or she might be thrown out of work in the next six months.

In the poll, 28 percent said that during the past year they or someone in their household had either lost a job, been forced to accept a lower-paying job or had paychecks reduced because of a forced decrease in working hours. One result of this is the criticism citizens aim at Reagan: 64 percent said they disapprove of his handling of unemployment, 26 percent said they approve. In the so-called "presidential popularity rating," Reagan showed a slight increase, with 49 percent saying they approve his handling of the job, compared to 46 percent last month.