President Reagan said yesterday that the federal minimum wage "should never have been applied to young people" seeking summer and after-school jobs, and that "the right thing to do" would be to eliminate the minimum wage for them. But he said it would be "hopeless" to send such a proposal to Congress.

The administration recently proposed reducing the minimum wage to a "sub-minimum" for youths in summer months, saying it would allow more young people to find jobs. Other Republican administrations have also proposed sub-minimums, which organized labor has regularly opposed as a threat to one of its most basic protections.

Reagan's new suggestion of dropping the minimum entirely goes even further, and is likely to be even more controversial.

The wage idea was one of two presidential remarks that created a stir yesterday. The other came in a transcript in which Reagan told editorial writers on Tuesday he had decided to ask federal agencies to accelerate already scheduled federal construction and maintenance work as a way of creating jobs and reducing the unemployment rate.

But White House spokesman Larry Speakes insisted afterward that the president has not made a decision. The "correct interpretation" of Reagan's remark, Speakes said, is that he has not yet signed off on the proposal.

And congressional aides said the administration has hardened its resistance to any jobs program that will add to the federal deficit since last Friday's news that unemployment fell in January from 10.8 percent to 10.4 percent.

Reagan's minimum-wage remark was the second off-the-cuff suggestion he has made in recent weeks about major policy shifts not yet specifically endorsed by his own administration. Previously, Reagan called for elimination of the corporate income tax. The White House then backed away from the idea.

On the minimum wage, the administration plans to ask Congress to reduce the current $3.35-an-hour rate to $2.50 for everyone under the age of 22 between May 1 and Sept. 30 each year. Justifying this proposal yesterday, the president said, "The line on the chart of unemployment for teenagers, the young people, goes right along increasing with the increase in the minimum wage."

Reagan, noting that teen-aged workers tend to be unskilled, said the current minimum wage makes the jobs "too expensive" for employers to fill. This argument has often been made by conservatives who support a sub-minimum wage as a way to reduce the high unemployment rate among teen-agers, particularly blacks.

But those who oppose the sub-minimum wage, including Democrats and organized labor, say it would throw older workers out of jobs and unfairly discriminate among workers.

"There is a long tradition in America of equal work for equal pay," said Rep. George Miller (D-Calif.), chairman of the House labor standards subcommittee. "Before Ronald Reagan looks to the schoolyard for a solution to the unemployment problem, he should look at their parents who are standing in line in hiring halls."

Reagan went beyond his administration's proposals on the minimum wage yesterday. He said he has "believed for many years" that the minimum wage "is really based in mind of the mature employe" and "should never have been applied" to young people.

In the Tuesday remarks to editorial writers, the president said, "Now, what we have said to all of our agencies and departments is that the budgets for all of them, their maintenance work, construction, things of that kind that are called for, and what we've said, 'Expedite it. Accelerate it. Don't wait if you've got it on schedule some place down the line. It's already in the budget. It won't add anything to the deficit to do it. Go to work on it and start doing it to help in the recovery.' "

However, Speakes later said, "The correct interpretation of what he was saying is that he has authorized the OMB Office of Management and Budget to make a survey of agencies and the budget and look into the budget to see what can be accelerated. But it would be more or less straining, going a little too far, to say he has agreed up or down . . . . "

On Tuesday, White House Chief of Staff James A. Baker III and key aides gave the president a list of government projects that could be done sooner than planned in order to create jobs and lower the unemployment rate, according to Speakes. The list did not include an estimate of the cost of the program or how many jobs it would produce, but it did raise the possibility of immediately starting projects scheduled for the next fiscal year.

Meanwhile, congressional aides reported yesterday that the administration now appears less receptive to the idea of a jobs bill than it did a week ago.

"They were ready to listen, particularly to the Republican bill, but now they don't see the need to compromise," said one Republican Senate aide.