Soviet commanders have told their troops to expect to stay in Afghanistan for two years, government officials disclosed yesterday.

This information from Afghanistan signifies that the Kremlin has concluded it will take at least that long to quell the rebellion in that country, rebuild the Afghan army and install an acceptable government.

Sources said that the two-year estimate represents a change, because the Soviets originally hoped to make a quick fix in Afghanistan and withdraw troops by this summer.

The recent notification to troops about two-year tours comes on top of other evidence that the Soviets are digging in for a long stay in Afghanistan. Understrength units in the Soviet Union near the Afghan border are being beefed up, and war stocks there and in Afghanistan are being increased, sources said.

The U.S. government estimates there are about 80,000 Soviet troops in Afghanistan and 30,000 others in bordercamps. Soviet dissidents are passing the word to U.S. officials that Russian families are becoming alarmed about the ferocity of the fighting in Afghanistan.

One report from Afghanistan obtained by U.S. officials asserts that some Soviet troops have been mutilated.Dead Soviet soldiers have been found with their noses and ears cut off,according to this report.

Washington Post foreign correspondent Kevin Klose reported from Moscow Feb. 28 that "there are rumors that some of the dead have been so badly mutilated that their coffins were permanently sealed." He added that some western officials in Moscow estimated that as many as 5,000 Soviet soldiers had been killed or wounded in Afghanistan since the Soviets invaded last Dec. 27. U.S. sources estimated that 100 Soviet soldiers are being killed there weekly.

The Soviets' new battle plan, by U.S. reckoning, calls for sending an additional two divisions of 10,000 to 15,000 troops each into Afghanistan soon to start the spring offensive. The buildup will continue until the Soviets have about 130,000 troops in country, U.S. analysts predict.

These troops, with the big punch from helicopter gunships, armor and artillery, will be more than enough to crush any organized rebel forces in Afghanistan, these analysts believe. The harder job, they predicted, will be installing a government the Soviets can depend on.

It is this part of the task, officials reasoned yesterday, that impelled the Soviet high command to decide on two-year tours for their troops in Afghanistan.

The prospect of a two-year occupation all but dashes any hopes the Carter administration may have held fora quick Soviet withdrawal from Afghanistan.

President Carter has urged the U.S. Olympic Committee to boycott the Moscow Games this July to protest theSoviet invasion. The committee has been cool to this plea.

As recently as last month, U.S. sources said, Soviet Ambassador Anatoliy F. Dobrynin was saying at Washington cocktail parties that Soviet troops would be out of Afghanistan by the time the Olympics opened.

Although the notifications about troops remaining in Afghanistan for two years underscore the prospects of a long stay, U.S. officials yesterday cautioned against calling the operation Russia's Vietnam.

The big difference, they said, is that the Soviets will be sustaining a war just across their border -- not 10,000 miles away as was the case with the American involvement in Vietnam.