Democrats trying to change emphasis of Pentagon's budget. Aspin says Democratic plan must not be seen as weak alternative

The Democrats are not soft on defense. That is what House Democrats want to prove as they launch an alternative to President Reagan's defense program.

Next week they will propose an amendment to the 1986 defense authorization bill now working its way through the House. This will be aimed not at saving money, but at changing the priorities in the defense program -- including shifting emphasis away from nuclear to conventional forces.

``The net effect of the package will be a near wash in terms of money,'' says Les Aspin (D) of Wisconsin, chairman of the powerful House Armed Services Committee, who is spearheading the drive. ``We're just reordering priorities -- not saving money.''

The alternative would:

Provide full funding to research the make-or-break elements of the President's Stategic Defense Initiative, (known as SDI or ``star wars'') but slow down work on systems that may violate the 1972 Antiballistic Missile (ABM) Treaty. That agreement limits missile defense testing and deployment.

Permanently cap deployment of the 10-warhead MX missile at the number already approved -- 40 -- but accelerate funding for the Midgetman missile. It is a one-warhead land-based mobile missile deemed to be more survivable than the MX.

Put a moratorium on the testing of antisatellite weapons in space (as long as the Soviets follow suit) and increase funds for research on protecting US satellites.

Increase funding for improvements in conventional forces, including sealift capability, ammunition, and ``smart'' weapons, with savings from cuts in SDI and MX.

The House Democratic alternative comes after the first-round efforts in the Senate to scale back or restructure SDI failed. Senate Democrats and Republicans who have misgivings about the purpose and feasibility of SDI back similar revisions in the program.

Behind these efforts to alter the administration's spending priorities lies a growing concern about the impact of the President's SDI program on the arms control talks in Geneva. The lawmakers do not rule out the need to proceed with research on the visionary program, which aims at a space-based, nonnuclear shield to make nuclear weapons obsolete.

``It's too appealing a possibility to dismiss without examination,'' says Mr. Aspin of the SDI program, ``but at the same time it's too big a change in the way we think about security to adopt as doctrine overnight.''

SDI would change the doctrine of deterrence by gradually giving up offensive nuclear weapons for a defensive system. Its introduction into the arms control process has greatly complicated achievement of an agreement.

The Russians insist they will never conclude an accord as long as the US pursues SDI, while the administration insists that SDI is only a research program and not negotiable.

Democrats and some Republicans want to shape SDI funding in such a way that it poses a smaller obstacle to an arms control compromise in Geneva.

Under the Aspin alternative, SDI research would be divided into three broad categories.

Elements of the program which would determine the ultimate feasibility of SDI would be fully financed. This includes research into system survivability, computer and other ``battle management'' problems, and the overall ``architecture'' of the system.

On the other hand, technology that threatens to bump up against the ABM treaty would be funded at a lower level. Such technology would include airborne optical systems, space-based tracking lasers, hypervelocity guns (so-called ``rail guns''), and kinetic-kill vehicles.

Funding for all other SDI systems would be increased by 35 percent or so over fiscal 1985. The Aspin alternative on SDI -- which will be embodied in an amendment presented by Rep. Norman D. Dicks (D) of Washington -- would cost between $2.1 billion and $2.5 billion. The President has asked for $3.7 billion, and the Senate last week moved toward approval of a $2.7 billion budget.

``I don't think [SDI] is going to work,'' Mr. Aspin told reporters at a breakfast meeting Thursday. But, he says, he would spend money to find out if it did.

Democrats, says Mr. Aspin, cannot get votes if the American public perceives they are soft on defense.