President Carter's actions since his address to the nation three weeks ago appear to have caused conflicting and sometimes sharp changes in public perception of him, according to the findings of a new Washington Post national poll.

Based on interviews two and three days after his July 15 televised speech and re-interviews with many of the same people last week, Carter seems to have both lost and picked up support on large-scale but equal levels.

His repeated criticism of Congress apparently has lit a spark far more than has his Cabinet purge. The poll suggests strongly that a majority of the public is concerned that a widely perceived clash between Carter and Congress has resulted in governmental paralysis.

The Cabinet shakeup, in which five Cabinet members resigned or were fired or reassigned, was seen by an almost 2-to-1 ratio among the public more as a political move to help Carter than in the terms Carter used to describe it - a means of creating an administration that is more unified and better able to deal with the nation's problems.

But for every person who appeared unhappy with Carter for playing politics with his Cabinet, there seemed to be another who thought such a move was overdue, according to the poll.

The net short-term effect of all this is a standoff. About 30 percent of those polled gave Carter lower job ratings last week than they had two weeks earlier, but another 30 percent gave him higher ratings. The result was that he edged from a position of 5.0 to 5.1 on a scale of 0 to 10 - representing no overall change at all.

Against potential political opponents such as Sen. Edward M. Kennedy (D-Mass.) and Ronald Reagan, once again there was a striking change in the movement of support to and away from Carter.

In the two weeks between interviews, 40 percent of those polled who identified themselves as Democrats moved either to or away from Carter as the preferred party nominee for president in 1980. More than 45 percent of all people who said they were registered voters moved either to or away from Carter in a hypothetical presidential race against Reagan.

Overall, the matchups show no change from mid-July to the beginning of August. Among Democrats, Carter still trails Kennedy by 2 1/2 to 1; among all registered voters he ran even against Reagan in the first test and he continued to run even in the second one.

Findings like these may be read to mean that not much is going on politically, that public attitudes are soft. Conversely, they may reflect real volatility. Polls often lend themselves to such alternate, conflicting interpretations.

In the matter of Carter and Congress, however, there is clearly widespread public concern, if not outrage. In his speech July 15, when he presented a new energy program and spoke about a national "crisis of confidence," Carter referred to Congress as being "twisted by special interests."

In a news conference 10 days later, he urged citizens to express their views on the nation's energy problem to members of Congress. In a nation where one-third of the population had so recently had to wait in long lines to buy gasoine, that criticism and focus on Congress were not missed.

Asked whether they felt Carter and Congress generally have worked well together, not worked well together or whether that was a subject they hadn't formed an opinion on, two-thirds of those polled last week said Carter and Congress have not worked well together. Twice as many people, 35 percent to 17 percent, blamed Congress as blamed Carter for that. The largest single block, 39 percent, said Carter and Congress were equally to blame.

A follow-up question to those who said Carter and Congress have not worked well together asked whether the lack of cooperation was harmful to the nation, good for the nation or whether it didn't make much difference for the nation. Eighty-six percent said it was harmful.

"Congress and Carter seem to be playing a game of politics," said a 25-year-old telephone company worker from Montville, N.J., one of those polled who blame both Carter and Congress for the perceived problem. "It's harmful because nothing is getting done."

In all, almost 6 in 10 Americans feel that the national interest is being damaged by the failure of the president and Congress to work well together, according to the poll.One example of the kind of harm envisioned lies in public expectations about what Congress will do with Carter's proposed energy legislation.

Asked last Tuesday and Wednesday whether they thought Congress would act quickly on the energy package, an overwhelming 62-to-24 majority said Congress would not act quickly, with 14 percent expressing no opinion.

By a 5-to-3 ratio, those interviewed said they expected Congress to change a great deal of Carter's energy program rather than make only small or minor changes. Among those who expected Congress to revise the legislation, only one-third thought the lawmakers would end up improving it.

Shortly after the poll interviewing ended last week, the House made vast changes in parts of the energy bills, drawing renewed criticism from the White House.

On Friday, Congress recessed for August without taking any action on the measures. Judging from those actions, it does not appear that Carter's call to the public to exert pressure had any favorable impact on Capitol Hill.

Congress' failure to respond quickly to Carter's demands may prove unpopular with the public, but it also may be politically damaging to the president. Repeated failure by him to budge the legislative branch could make him appear ineffectual, lacking in leadership - the number one public complaint about Carter.

"Lyndon Johnson and Gerald Ford knew about how to deal with Congress, but not this one," said a businesswoman in Holland, Mich., who was interviewed by The Post. "I think President Carter is too inexperienced to be able to communicate with Congress."

On the other hand, there are signs that Carter may be making some gains from his criticism of Congress. The Post Office at the Capitol reported Friday that it had received a substantial increase in mail after Carter's July 15 speech, and especially after his later request that the public express its views to Congress on the energy problem.

There was no great outpouring, such as during the Panama Canal treaties debate last year, but rather an increase of up to 45 percent above the usual amount of mail received.

Furthermore, the poll suggests that there is a decided trend on the part of many to be more sympathetic to Carter than to Congress. In the first interviews, people were evenly divided when asked whether Carter or Congress was doing a better job in handling the country's problems. One-quarter chose Congress, a like amount chose Carter and the rest chose neither.

The finding in the second interviews - that twice as many people blame Congress as blame Carter for their perceived failure to work well together - suggests a sharp turn in Carter's favor.

The political importance of such a turnabout is major: people who feel Carter is being victimized by Congress are much more likely to support him in an election than are those who think he is largely or equally to blame for his problems with Capitol Hill.

In other areas, The Post's poll made these findings:

Carter was seen "doing as well as most presidents could do to cope with inflation and the economy" by 49 percent of those interviewed, doing worse than most by 32 percent and doing better than most by 13 percent.

On the energy problem, he was seen "doing as well as most presidents could" by a similar 49 percent, doing worse by 27 percent and doing better by 17 percent.

In trial heats against Republicans other than Reagan, Carter outpaced John Connally by 55 percent to 28 percent, with 17 percent undecided, and Sen. Howard H. Baker J. (R-Tenn.) by 47 to 31, with 22 percent undecided. Carter trailed Ford in a similar trial heat by 42 to 47 percent with 11 percent undecided.

Forty-eight percent of those interviewed said they like it when Carter talks in moral or religious terms, 31 percent said they felt he was too preachy, and 11 percent said they like his use of moral and religious terms but felt that he sometimes overdoes it.