At this point, the strong showing of Republican presidential candidate Ronald Reagan in the 1980 campaign is not reflected in support for Republican congressional candidates, the Gallup Poll says.

While the most recent Gallup test election shows Reagan far ahead of President Carter (as well as other Democrats tested) and independent candidate John B. Anderson, the Republican Party has not picked up any demonstrable strenght in races for Congress since surveys earlier this year.

The current national vote for the House of Representatives, based on the choices of registered voters, shows the Democratic Party with a 57-to-43 percent advantage over the Republican Party.

The previous mid-June survey showed the Democratic Party with a similar 58-to-42 percent lead, the same as recorded in a late February-early March poll.

In the latest presidential trial heat, Reagan is the choice of 45 percent of registered voters to 31 percent for Carters and 14 percent for Anderson.

These findings conflict sharply with conclusions drawn by pollster Louis Harris last week when Harris said the Republicans conceivably could take control of Congress in November.

In addition, Gallup finds Reagan and Carter race closer than does Harris, and gives Anderson significantly less voter strength at this time. The Gallup and Harris polls were taken at the same time.

There are two apparent reasons for the differences.

First, Gallup's sample is made up of people who say they are registered voters, while Harris describes his as consisting of "probable voters." The Gallup sampel includes 40 percent Democrats, 27 percent Republicans and 24 percent independents. The Harris sample has more Republicans in it. Thirty-nine percent of his probable voters are Democrats, 32 percent Republicans and 26 percent independents. By interviewing more Republicans, Harris naturally draws conclusions more favorable to the GOP.

Second, the new Harris poll had eight questions dealing with Carter's handling of the presidency directly preceding the questions about how people might vote in the presidential race. Some pollsters contend that such a question order creates bias. For example, one prominent pollster for GOP candidates said the question order used by Harris "could bounce the results by 10 points."

Generally speaking, polls at this time in an election campaign are not accorded a great deal of significance. This year, however, poll findings have been central in the unsuccessful efforts to dump Carter at the Democratic nominee. The polls most often cited are those by Harris which have suggested that not only would Carter lose in November, but he stood to carry a good many other Democrats down with him.

While the Gallup national vote for Congress cannot be translated directly into House seats, it is difficult to foresee any major changes in the present composition of the House -- 275 Democrats and 159 Republicans.

Harris' latest findings are that in a three-way race, Reagan leads Carter, 48 to 28 percent, with Anderson at 19 percent

He finds Reagan ahead in every region of the country by fairly uniform margins. In the South, Reagan is ahead of Carter by 52 to 32 percent, with Anderson at 12 percent. And in the big, electorally rich northern states Carter is running third behind Anderson. In eight of the biggest states outside the South -- California, New York, Pennsylvania Illinois, Ohio, Michigan, New Jersey and Massachusetts -- Reagan has 44 percent of the vote, Anderson 26 percent and Carter only 25 percent.

When Harris asked voters how they would cast their ballots in November if polls show Anderson had a chance of winning, Reagan's lead was cut to 42 percent, Anderson jumped to 30 percent and Carter trailed with 25 percent. Before the president's Aug. 4 press conference, Reagan led with 46 percent, Anderson had 30 percent and Carter had 22 percent. Thus, events of last week saw Reagan losing four points and Carter gaining three, with Anderson holding firm with his 30 percent.