Troops may go, but Soviet Afghan legacy remains. HOMEWARD BOUND

Moscow will meet or come close to its promise of halving its forces in Afghanistan by Monday, the Reagan administration concludes. But on the eve of the key Aug. 15 deadline - marking three months of the historic withdrawal accord - one top US official warns that Soviet compliance is generally a ``mixed bag.''

This is particularly so because of recent Soviet offensive military actions. (Resistance steps up pressure, P. 8.)

``Our best guess is that the Soviets will have about 50,000 troops out of Afghanistan or on the road by Aug. 15,'' a well-placed US official says.

The 50,000 troops represent half the troops that Moscow admits were in Afghanistan when the accords took effect May 15. But the figure falls about 7,000 troops short of half the US estimate of Soviet forces present in May.

Nevertheless, a few US officials think Moscow may meet even the 57,000-troop figure. All of those queried explain that Washington has only limited ability to accurately measure Soviet troop presence in the short term, which makes US estimates fuzzy.

A range of top US officials say in the broad sense the Afghanistan accords are working well. The Soviets are leaving, their Afghan allies are weakening, and the accords have set the tone for superpower cooperation in solving other regional conflicts.

During his recent visit to the Soviet Union, Secretary of Defense Frank Carlucci III received firm assurances from the Soviet defense hierarchy that the Soviet Union is committed to pulling its troops out of Afghanistan fully and honoring the Geneva accords, informed officials say.

Other messages and intelligence reinforce those commitments, they say, but that doesn't mean the Soviets are not looking for ways to boost their sagging Afghan allies as they leave.

``The Soviets don't seem to have yet drawn the basic conclusion that the PDPA [People's Democratic Party of Afghanistan] must yield the monopoly of power and allow real self-determination,'' a top US official says. ``So the only way that will happen is for the mujahideen to continue to fight for it. And the US will continue to support them as long as Moscow supports its allies.''

In this context, says the well-placed US official, ``our concern is not so much the Soviets meeting the 50 percent goal as it is the offensive operations which the Soviets are carrying out.''

Before the Geneva accords were signed, the Soviets said they would not conduct offensive operations during the pullout, except to defend themselves. In recent weeks, however, Soviet planes and troops have carried out a number of offensive operations to support their Afghan allies in places where Soviet troops had earlier withdrawn, US officials say.

A Soviet plane, for example, was recently shot down 10 miles inside Pakistan. ``These operations are clearly designed to intimidate the mujahideen and Pakistan,'' a senior official says.

Moscow has been complaining vigorously about ``violations'' of the Geneva accords by Pakistan and the US. The complaints center on the continued provision of arms and political support for the Afghan guerrillas. However, the US made clear at the time the accords were signed that the arms flow to the guerrillas would continue as long as Moscow continued to aid its Afghan clients similarly.

The root of the Soviet complaints, US officials say, is the relative military success of the guerrillas against the Afghan communists.

``The mujahideen are doing much better than the Soviets thought they would ... and succeeding far better than even I would have thought a year ago,'' says Rep. Charles Wilson (D) of Texas, a longtime mujahideen supporter who recently conferred with the resistance leadership in Pakistan.

US officials say the Soviets have supplied large numbers of armored vehicles and artillery to their clients since May 15 in an effort to help the regime hold and resupply garrisons.

``Moscow would claim this isn't interference in Afghanistan, but we say this is as much interference as any aid which might be coming in from Pakistan,'' a key official says.

US officials add that the Soviets and their allies continue to lay mines and refuse to dismantle the massive mine fields put in place earlier. ``The mines are more of a deterrent to the return of refugees from Pakistan than any thing the government there is doing,'' adds the key official.

Officials say there is likely to be a hiatus in the Soviet troop departure after the Aug. 15 rush. The next benchmark is Feb. 15, when all troops are to be out. As a US specialist explains, once the remaining Soviet troops begin to leave, they will have to do so ``in one fell swoop'' or be very vulnerable to attack. But he says there is no logistical reason why all Soviet troops could not be out by the end of the year - a date mentioned earlier by Soviet Foreign Minister Eduard Shevardnadze.

Administration sources stress that their goal is not to humiliate Moscow. ``We recognize how hard it is to leave one's allies behind from our experience in Vietnam. But there is no evidence the Soviets are yet preparing the way for future change that will surely come,'' one official says.

US officials say they want the accords to work, not only for Afghanistan, but because success will encourage further superpower cooperation in other areas of the world. ``The Soviets are essential players in resolving many of the world's trouble spots. We can already see the benefits of improved dialogue in southern Africa and elsewhere,'' says a ranking official. But Washington will not let Moscow off the hook in Afghanistan, he adds.

Some US conservatives are worried, however, and pressuring the administration. Sen. Gordon Humphrey (R) of New Hampshire is holding up confirmation of two ambassadors so as to get administration cooperation in appointing a special presidential envoy to the Afghan resistance.

Senator Humphrey says that the US is not giving the resistance enough sophisticated weaponry to meet the Soviet challenge and that Washington should give the resistance higher diplomatic recognition.

Senior administration officials say the resistance has more than enough weapons. Whatever it has received from the outside has been multiplied by the large weapons caches captured in recent months.

Representative Wilson returned from his trip to the region with the same impression: ``I have no heart burn about their needs. They have lots of material piled up.''

The administration also opposes the idea of a special envoy. It has just named a special assistant to the US ambassador to Pakistan who will follow Afghan events.

But senior officials explain that the US should not get into the business of anointing the current alliance leaders as an alternative regime. ``We don't know enough to say who is a bad guy and who is a good guy among the resistance, and for centuries outsiders have repeatedly failed in their attempts to mold Afghan politics to their liking,'' a ranking official says.