Treasury Secretary-designate W. Michael Blumenthal said yesterday that jobless rates of either 4 or 5 per cent are "too high" as national goals for full employment and that the best goal is zero unemployment.

But he conceded that the need to be "careful and prudent" would prevent the incoming Carter administration from reducing the jobless rate below 6.5 per cent to 7 per cent if we are lucky."

The current rate is 8.1 per cent.

Preventing a more dramatic program is not the danger of inflation, he said, but a limitation on how much stimulus the economy can absorb in short order. As the Carter program takes effect, he predicted, there will be further "steady reductions" in the jobless rate in 1978.

Interviewed on "Issues and Answers" (ABC, WMAL), Blumenthal also:

Said the stimulus packages announced Friday in Plains, Ga., is only "the first step in a more fundamental set of proposals for tax reform."

Emphasized that the Carter administration would rely largely on the private sector for restoring health to the economy "because five out of six jobs are in the private sector."

The question about unemployment goals relates to an important and basic difference in the political approach to current economic problems. Early in the Kennedy years the Democrats adopted 4 per cent as an "interim" target for full employment.

In recent years, while many liberal Democrats have pressed to lower the target to 3 per cent, Republicans and other conservatives have argued that 5 per cent is more reasonable. They reason that with changes in the makeup of the labor force, to press for unemployment below that figure is likely to cause inflation.

Asked to name a realistic unemployment target in today's economy, Blumenthal responded:

"I am tempted to say the best goal is zero, or close to zero, and I feel strongly about that. In this great country of ours, richest in the world, there shouldn't be any people who want to work, and who are looking for work, and are unable to find gainful emplopyment. We can do so many things, we ought to be able to lick that problem as well."

He said that there is "no magic number," but that both 5 per cent and 4 per cent "I would consider too high."

Blumenthal, former chairman of the Bendix Corp., acknowledged that there will always be some "fractional" unemployment - people between jobs - but "it can be a lot lower than it is today."

Although the Carter package contains no specific new incentive for business to add to its investment plans, Blumenthal argued that the entire program is intended to encourage business expansion by creating additional consumer demands.

Other sources indicated that there may yet be some changes in the final Proposals made to Congress. One possibility is the substitution of an investment tax credit for the $2 billion credit against Social Security payroll taxes originally announced.

In a telephone interview yesterdayM economist Lawrence R. Klein, chairman of the economic advisory group during the Carter campaign, said he hopes the President-elect will go back to the investment credit idea "because we need more capital formation and the investment tax credit wouldn't hurt as a starter."Another possible change in the Carter economic package may be in the amount of public works spending that will eventually be proposed. On "Face the Nation" (CBS, WTOP) yesterday, Senate Majority Leader, Robert Byrd (D. W. Va.) made a flat prediction that Congress would add to the $2 billion that Carter proposed for public works.

He strongly implied that Carter had agreed with the Democratic leadership on this point during their discussions Friday at Plains.

Blumenthal predicted that the administration would send its tax reform proposals to Congress within clender 1977 for action in19 1978, and that the proposals would stress simplification of the tax code and procedures.

He also revealed that not all of the 700,000 to 800,000 public service jobs contemplated in the Carter program would be on the government payroll, since private organizations in some cases would receive the funds to carry out thetraining programs.