STATELINE, Nev. (AP) _ Political leaders from 15 Southern states unanimously approved a plan Wednesday to coordinate presidential primaries and caucuses to give the area more clout in picking nominees for president in 1988.

''We're the ones who will be creating the waves instead of some of our smaller Northern and Midwestern brothers,'' Democratic state Sen. John Traeger of Texas said after the vote.

The Southern Legislative Conference, made up of leaders of 15 state legislatures, voted to hold presidential primaries, caucuses and delegate- select ing conventions in the second week of March in 1988.

Although the action is not binding, legislators from all 15 states said that they would seek necessary changes in election laws and that in every state they had bipartisan support of key political leaders.

''We don't have to wait until some far distant date in the future,'' said Traeger, who chairs both the conference and the task force that drafted the plan for the ''super primary.''

''It can be done right away. It's a bipartisan effort, and one which we think will be of equal value to both parties.''

Under the resolution, the 1988 primaries, caucuses and conventions would be held Tuesday, March 8, 1988, or on the following Saturday, March 12.

The Southern lawmakers met on the eve of the national convention of the Council of State Governments at the same hotel where where Eastern, Midwestern and Western lawmakers were holding their regional conferences preceding the national convention.

Leaders of the other three conferences said they expected no immediate attempt to either try to block or copy the southern ''super primary.''

''There is not the homogeneity you have in the South in any other region of the country,'' said Republican House Speaker Charles Hebner of Delaware.

''It certainly gives the southern states more clout than other regions. It may knock out early candidates who are a little more liberal - in both parties,'' Hebner said.

Speaker Pro Tempore John Connors of the Iowa House, vice chairman of the Midwestern Legislative Conference, noted that the plan was aimed at trimming the influence of his state's first-in-the-nation presidential caucuses, held in February.

The plan would include Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia and West Virginia.

Arkansas lawmakers had abstained from endorsement of an earlier proposal because of conflicts with other state elections, but state Sen. Charlie Chaffin said Wednesday that ''Arkansas feels it can overcome its problems. I feel reasonably sure Arkansas will adopt March 8.''

''I am convinced that our action will have a major and lasting impact on the process by which we elect the president of the United States,'' Traeger said.

Current laws in Alabama, Georgia and Florida already call for their primaries on the second Tuesday of March, and Oklahoma has also picked March 8 for its 1988 caucuses, giving the South a strong start on a regional primary.

Politicians from most of the other 11 Southern states said Wednesday they will introduce bills in their Legislatures next year to schedule their primaries or caucuses on March 8 or 12.

If all the Southern states adopt the same dates, nearly one-third of the delegates for both the Democratic and Republican conventions would be picked in the South in a five-day period, presumably forcing candidates in both parties to drastically revise their strategies and priorities for the all- important early momentum.

In 1984, Alabama, Florida, Georgia and Oklahoma were among 10 states picking delegates on so-called ''Super Tuesday,'' March 13, but the Southern states accounted for just half the delegates picked that day, and the rest of the South's primaries and caucuses were scattered over seven other dates from March 17 through June 5.

Southern leaders said the plan would force presidential candidates in both parties to pay more attention to Southern political priorities.

''The goal of increased Southern influence in the nomination process is especially appealing to Democratic state leaders,'' a conference report said. ''... Despite the overwhelming Democratic registration in the South, Republican presidential candidates have won the South in four of the last five elections.

''Nevertheless, the movement is nonpartisan, and with the Republican nomination wide open in 1988, Southern Republicans ... also want to increase their influence in choosing a nominee,'' the report said.