Administration supporters in Congress have become more optimistic about the chances of passing the President's "Youth Corps Bills" since the Senate approved the first of the measures Wednesday night.

It was not the margin of the 50-34 victory of the Youth Employment Bill that impressed the proposal's backers, but the support the measure won from Southern Senators; Olin Johnston (D-S.C.), George Smathers (D-Fla.), Russell Long (D-La.), Estes Kefauver (D-Tenn.), all voted for the bill.

Support from Southerners will be necessary if the bill is to pass the House. Last year the Rules Committee blocked a similar bill by an undisclosed vote, and this year's proposal must win the support of Rules' three Southern Democratic moderates if it is to reach the House floor.

Five Democrats will probably support the measure in the committee; five Republicans, along with chairman Howard Smith (D.Va.) and Rep. William Colmer (D-Miss.) are certain to oppose it.

Three Decide Fate

The votes of Rep. Carl Eliot (D-Ala.), Rep. Homer Thornberry (D-Tex.), and Rep. James Trimble (D-Ark.) will decide the fate of the bill. The three are ordinarily Administration backers, but sentiment against the bill in their districts may force them to oppose it.

But if the vote of the Senate's Southern moderates is any indication, Rules may be expected to clear the bill. If the proposal ever reaches the House floor. Democratic leaders believe they have a better than even chance of getting it passed.

The Senate vote also made Administration supporters more confident of passing the Domestic Pence Corps Bill, which would send skilled volunteers to do social work in depressed areas. "If we get the same Southern support, I'm sure the bill will pass the Senate," one supporter said.

Two "Youth Corps"

The Youth Employment Bill would establish two "Youth Corps": a Youth Conservation Corps modeled on the depression-time CCC to work on federal conservation projects, and a Home Town Youth Corps, whose members would do social work in their home towns.

The YCC would have 15,000 enrolees the first year and the Home Town Corps 50,000; after the first year Congress would decide the number of members.

Those backing the bill hope to combat unemployment by teaching the Corps volunteers useful trades while they are enrolled. Republican Congressional leaders have said that the measure does not lay enough emphasis on job training, and called for a different approach to the problem of joblessness among teenagers. Members of both Corps would have to be between 16 and 21.

Amendments on the Senate floor cut the funds for each Corps from $60 to $50 million and restricted enrollment in the Corps to "persons of good character."

Sen. Edward M. Kennedy (D-Mass.) made his first speech on the Senate floor in opposition to the latter amendment. Kennedy argued that the provision might keep school dropouts or men with petty criminal offenses on their records out of the Corps