Louisianians can elect today a U.S. senator and members of Congress, but these political battles have been overshadowed by last night's heavyweight championship fight in the Louisiana Superdome.

This has happen not only because of the aura, celebrities and money surrounding Muhammad Ali and Leon Spinks but also because the campaigns generally have been unemotional.

Rep. David C. Treen (R-La.) escaped opposition altogether in the 3rd congressional district and Sen. J. Bennett Johnston and the other six Louisiana House members running for reelection are expected to win easily.

The principal House contest is for the seat being vacated by Rep. Joe D. Waggonner (D-La.). Because the district in Northwest Louisiana is highly conservative, it has been regarded as ripe territory for a Republican, who would become the fourth member of his party in the states eight-person House delegation.

Even though today's election is a primary, Republicans, Democrats, candidates from other parties and independents are in the race because Louisiana has an "open primary" system that puts each candidate for every office on the ballot.

For example. James Wilson of Vivian, a Republican, is running for Waggonner's seat against Democrats Charles E. Roemer III of Bossier City and Claude Leach Jr. of Leesville. Roemer, the son of Gov. Edwin W. Edwards' chief of administration, has a slight edge because of his father's name, but no one is expected to poll the 50 percent needed to win outright today.

Runoffs resulting from today's balloting will be held Nov. 7, general election day elsewhere in the country.

In a general election, representatives of different parties would run against each other and independents for the first time. But with Louisiana's "open primary" system, it is conceivable that two Democrats could be opposing each other for any office on Nov. 7.

Because of the contest for Waggonner's seat, voter turnout is expected to be high in that part of the state, and that should benefit Johnston, who is running for his second term against state Rep. Louis (Woody) Jenkins of Baton Rouge. Johnston is a native of Shreveport, which is in Waggonner's congressional district.

In addition, Johnston is relying on his incumbency and his high name recognition in New Orleans, Louisianaist biggest city. He is expected to capture votes from blacks, labor and liberals, even though he always has characterized himself as a moderate-to-conservative politician.

In his campaign, Jenkins, a conservative who supported George Wallace in the 1976 presidential election has painted Johnston as a free-spending liberal and has forced the senator to take more conservative stands than he already does and to stress such things as his votes for national defense and frugality in government.

However, Jenkins' attacks are expected to have little effect on Johnston's ability to win.

The other races for congressional seats are expected to result in easy victories for incumbents.

They are Robert L. Livingston Jr. (R) in the 1st Congressional District. Lindy Boggs (D) in the second, Jerry Huckaby (D) in the fifth, W. Henson Moorse (R) in the sixth, John B. Breaux (D) in the seventh, and Gillis W. Long (D) in the eighth.