Does job-training pay its own way?

Is job training for the poor basically just welfare or is it an investment that pays?

If the Reagan administration succeeds in replacing the nine-year-old Comprehensive Employment and Training Act (CETA) with block grants to the states by the end of this year, as it hopes, the states will be searching hard for the right answer to that question.

David Shulenburger, associate professor of business at the University of Kansas, has recently completed a study of CETA workers in Kansas. He says his findings bolster the argument that CETA is an ''investment.''

He and research associate Judith Sardo looked at the effect of CETA training on participants' income during two three-month periods in 1979 and 1980. They measured the pay history of CETA-trained workers against the pay of those in two control groups who received no CETA training. The results:

* They found that the average income of those trained under CETA was 65 percent more than those who had no CETA help.

* They found also that the state regains the money invested in CETA training in about seven years time through increased tax income and decreased unemployment insurance and welfare payments. Indeed, in the earlier 1979 period when the economy was more robust, the investment essentially was returned in less than three years.

''Some think the only justification for this kind of job training is a humanitarian instinct,'' observes Dr. Shulenburger. ''But we've got to start thinking of it as an investment. If this target group doesn't get marketable skills, they will still be on welfare when the economy improves. Reintegrating them can yield more production at lower cost and keep wages from rising too rapidly. It seems to me to be nothing but a win situation.''

In general, there is widespread support for more and better job training as an answer to US unemployment. A recent Newsweek poll conducted by the Gallup Organization found that 59 percent of those queried felt federal spending for job training should be increased. At a press conference earlier this year, President Reagan himself mentioned pages of want ads he'd been reading in a newspaper and pledged to do ''everything we can'' to help people qualify to apply for such jobs.

But CETA, the nation's chief job-training program for the poor, has been so criticized over the years that no one is talking of continuing it without reform. It has been accused of failing to make long-term employment gains for clients, training clients in unmarketable skills, and even of outright fraud and hiring abuses. Much of the criticism centers on the way the program changed in the mid-70s when President Ford asked Congress to set up some 750,000 public service jobs as a recession aid. Cities used the extra hands for everything from street repairs to mayoral help; some of those employed were not traditional CETA candidates.

''It was a mistake to mess up a good training program - it did a real disservice to CETA and changed its character,'' Dr. Shulenburger says.

The public-service job part of the program was phased out last fall. CETA itself operates on a budget cut by two-thirds over the last two years and is slated to expire by Sept. 30.

Joint House-Senate Labor subcommittee hearings on CETA are scheduled to start on Capitol Hill March 15.

The administration is requesting a $2.4 billion job-training package for 1983 , including help for special target groups such as migrants and Indians and a continuation of the youth-focused Job Corps. Participants in the basic program, which would cost $1.8 billion, would no longer be paid a stipend while in training. Governors would be given the lion's share of the say in where training projects would be located in their states. The private sector would have a much larger role in deciding which skills are in short supply.

A bipartisan Senate bill introduced last month by Sen. Dan Quayle (R) of Indiana and Sen. Edward Kennedy (D) of Massachusetts also would allow governors to draw the project map. Under their plan, governors could hand the business community much of the planning authority that mayors now hold through existing private industry councils.

Overall, the Indiana senator's bill focuses heavily on youth (half the participants must be under 22) and has a relatively large $3.9 billion budget for fiscal 1983.

Two House bills also are up for consideration. One, sponsored by Rep. Augustus F. Hawkins (D) of California, would operate programs largely through local government. This plan has strong support from city and county lobbyists.