The Reagan administration plans to cut back funding sharply and reorganize two Labor Department programs that now provide jobs and training for about a half-million disadvantaged youth, sources said yesterday.

State and local governments would get greater flexibility but a lot less money in the administration of the programs.

Current administration plans are to create a block-grant jobs-training program by merging the Youth Employment Training Program and Youth Community Conservation Improvement Program with existing Labor training programs for adults.

Overall funding for these, which not totals about $3 billion, would be reduced by about $575 million.

The sources said the Labor Department also is planning spending reductions in staff for the Job Corps, although that program would be retained, and eliminating some federal aid for workers at state unemployment offices.

White House sources had indicated late last week that Reagan intended to reduce Labor's budget by about $900 million as part of a second round of budget cuts totaling about $10 billion throughout the administration. But they had not spelled out in detail where the Labor Department cuts would be made.

In the first round of cuts, the administration proposed the termination of 300,000 public service jobs, a federally funded program principally serving the hard-core unemployed adults, mostly in their 20s and 30s, who work in local governments and public and private social welfare programs as teacher aides, daycare center assistants, file clerks and maintenance workers.

About $746 million has been appropriated for the Youth Employment Training Program, which serves about 450,000 dropouts, high school graduates and youngsters 14 to 21, who are still in school.

It is the federal government's basic program for increasing the employability of disadvantaged youth. Local governments are already given broad say in how the program is structured in their areas, and they have used the federal dollars for remedial education, on-the-job training and union apprenticeship programs.

In the Youth Community Conservation Improvement Program, which received about $129 million this year, about 52,000 youth are put to work on such jobs as weatherizing and rehabilitating old houses and renovating parks.

The vast majority of youths in both programs are from families with incomes that put them at or near poverty levels. They receive allowances while in training and pay close to the minimum wage for their work in the jobs programs.

What the administration proposes to do is phase out both these programs by next fall and combine them with labor training programs for adults. Sources said local communities then would be given broad discretion on how to spend funds and could emphasize training for youth, adults or both, depending on the need.

About $2.1 billion is currently appropriated for the adult training programs. The administration is proposing a total of $2.4 billion for its new jobs training block grant.