The 15-month marathon race for Congress in Louisiana's First District ends Saturday.

Candidates for the post, which former Rep. Richard A. Tonry held for four months this year before resigning amid controversy over his election, are state Rep. Ron Faucheux, the Democratic nominee; Sanford (Sandy) Krasnoff, who bills himself as an "Independent Democrat," and Robert Livingston, the Republican nominee.

The district, composed of eastern New Orleans and nearby St. Bernard, St. Tammany and Plaquemines parishes, is 91.3 per cent Democratic, and Faucheux had been regarded as a clear favorite until last week.

The change in Faucheuz's fortunes came during a special session of the state legislature, when he voted against corporate and personal income tax increases to finance pay raises for teachers and other state workers. Faucheux justified his action by saying that the state already had enough money for the pay increases, but his vote cost him the backing of the Greater New Orleans AFL-CIO and two black political groups in New Orleans.

The AFL-CIO and the black groups switched their allegiance to Krasnoff.

Livington has also been gaining ground. According to his latest campaign finance report, he received more than twice as much in donations as Faucheux for the period from July 16 to Aug. 12.

Much of Livingston's money has come from out of state, including $1,410 from the national Republican Congressional Committee of Washington, $5,000 from the Fund for a Conservative Majority of Washington and a $5,000 loan from the National Conservative Political Action Committee.

If Livingston wins, he would become the third Republican Louisiana's eight-member House delegation. In addition to the state's two current GOP congressmen, David Reen and W. Henson Moore, Livingston has been helped by nationally known Republicans, including Ronald Reagan, whom he backed for president last year, former Treasury Secretary John Connally and former U.N. ambassador and Republican National Chairman George Bush.

All three have come here to speak at Livingston Fund-raisers.

Faucheux, who became the youngest legislator in the states's history when he was elected to the House of Representatives two years ago at the age of 25, stands to become the youngest member of the 95th Congress if he wins.

In this race, his age, combined with the fact that he is single and lives with his parents in eastern New Orleans, has become a major issue.

Faucheux and Livingston are both conservative members of their parties, while Krasnoff has staked out a more liberal position on several issues.

Even though oil is one of Louisiana's chief industries, Krasnoff has attacked "big oil companies" and has advocated divestiture of the bigger companies "to a degree," without advancing a specific plan.

In contrast, Livingston has called for governmental retrenchment, saying that Democrats in Congress "have over-regulated, over-taxed and over-controlled the average American citizen . . . We need to go up to Washington to cut back the bureaucracy."

During this campaign, the forgotten man has been Tonry, who won the seat last year in a come-from-behind race. However, 20 poll commissioners pleaded guilty to stealing votes for him in the Oct. 2 1976, Democratic primary and Tonry resigned in May.