Nearly two Americans in three now say President Reagan should abandon his program of tax and domestic spending cuts and try another way to revive the economy, according to a new Washington Post-ABC News poll.

At the same time, however, nearly three Americans in four say they would oppose tax increases to help reduce the federal deficit. A majority also would oppose reducing the deficit by reducing defense spending, but not so large a majority as has shown up in similar questions in previous polls.

The new poll also shows:

* An increasing general disapproval of the way the president is handling the economy.

* A 50-50 split on the question whether most Americans would benefit even if Reagan's economic plan "does what Reagan really wants it to do."

* A recent and marked decline in approval of Reagan's overall handling of the presidency and his conduct of foreign affairs.

On the basic approval-disapproval questions, the president draws lower ratings than in any other of the Post-ABC News polls since he took office.

In his Thursday news conference, Reagan said "it would be very foolish of us now to turn around and express a lack of confidence" in the program of tax cuts he pushed through Congress last summer. He also said there is "widespread support for continued cutting of government spending."

The new poll is at variance with that.

One question asked:

"Should Reagan stick with his economic program of cuts in domestic social spending and cuts in taxes, or should Reagan try some other program to help the economy?"

Only 35 percent said Reagan should stick with the program; 61 percent said he should try another. Among Democrats, three out of four said he should change; among independents, two out of three, and among Republicans more than one in three.

In earlier polls, majorities said they thought Reagan's economic program was hurting rather than helping the economy right now, but that they expected that it would succeed eventually. The new results suggest that this hope for the future may be fading.

A total of 1,004 adults were interviewed in the poll Wednesday and Thursday.

A majority of those interviewed, 51 percent, said they are opposed to cutting "spending for social programs to reduce the budget deficit," while 45 percent said they favor such cuts. Other Post-ABC News polls have shown opposition to domestic cuts increasing, but never a majority opposed.

On the other hand, by 72 to 21 percent, those interviewed said the government should not increase taxes to reduce the budget deficit.

The poll did not ask the alternative question: whether people approve or disapprove delaying, reducing or eliminating tax cuts scheduled to take effect this year and next. Many in Congress are proposing this rather than an outright increase in taxes to reduce future deficits.

Four in 10 in the new poll say the government should cut military spending to reduce the federal deficit, while just over half are opposed to such cuts. Those figures also suggest a decline in support for Reagan, following earlier polls that showed much higher majorities opposed to cuts in defense spending.

In recent months supporters and opponents of Reagan have noted a rise in the belief that Reagan's economic program is unfair, in that it hurts the poor and helps the rich. The new Post-ABC poll suggests that this belief continues to rise.

Question: "Do you think a majority or less than a majority of the people will be helped by Reagan's economic program if the program does what Reagan really wants it to do?"

Answer: 48 percent said a majority will be helped if it accomplishes what the president wants; 46 percent said less than a majority.

For the first time in a Post-ABC News poll, Reagan has less than majority support for his overall handling of the presidency. Forty-eight percent said they approve and 46 percent said disapprove. At the end of January, in the last Post-ABC News poll, 52 percent expressed approval and 39 percent disapproval.

Also for the first time, the number who said they "disapprove strongly" (28 percent) was higher than the number who said they "approve strongly" (24 percent).

As the other figures in the poll suggest, citizens gave Reagan a sharply negative rating for his handling of the economy, with 57 percent saying they disapprove and 38 percent saying they approve. In the January poll, Reagan drew an even 46 percent favorable, 46 percent unfavorable response for his handling of the economy.

And in the field of foreign affairs, the poll showed 40 percent saying they approve of Reagan's conduct and 41 percent saying they disapprove. In November, the last time the Post and ABC asked the public to rate Reagan on his handling of foreign affairs, approvals outpaced disapprovals by 54 to 35 percent.

Washington Post polling assistant Kenneth E. John contributed to this report.