The new Soviet-backed Afghan government has begun a campaign to spruce up its image at home and abroad, amid reports that the Soviet offensive against insurgent tribesmen is expanding into remote areas of the country.

"The Soviets are taking the war to the insurgents," one diplomatic source said. "They've moved off the main highways and they're going into the valleys."

Under a "general amnesty" decreed by the new Soviet-installed head of state, Babrak Karmal, the government yesterday released more than 2,000 political prisoners from the notorious Policharki Prison east of the capital. p

Meanwhile, there appeared to be no major changes in the military picture as Soviet divisions totalling by U.S. estimates at least 50,000 men -- and perhaps as many as 85,000 -- continued to deploy in the countryside in an offensive against Afghan rebels who say they are resisting a communist threat to their Moslem traditions.

In the capital, Soviet Troops continued to guard key installations they seized during the Dec. 27 coup, but at a much reduced level. Most units have moved into the provinces, and the Soviet presence here is scarcely noticeable. m

The unusual publicity organized for the release of prisoners seemed designed to divert international attention from the Soviet military campaign, about which little information is available.

Western journalists allowed into the country in the last few days were invited yesterday by the government to witness the releases, and television cameramen filmed emotional scenes as freed prisoners were greeted by a large crowd of relatives and friends.

However, some prison officials appeared not to have received the word to welcome reporters, and three members of an American television crew were detained for several hours after an argument over credentials with one newly installed bureaucrat.

Most Western reporters previously had been ordered expelled upon their arrival to cover the aftermath of the violent takeover.

Immediately after being installed in power, the new government began releasing jailed members of its Parcham (banner) wing of the People's Democratic Party of Afghanistan. They were imprisoned under the government of the slain president, Hafizullah Amin, who seized power in a coup in September 1979 from Nur Mohammed Taraki. Both Amin and Taraki belong to the rival Khalq (masses) wing of the party that came to power in a Soviet-backed coup in April 1978.

At the same time that Parcham members were being released from prison last week, the government reportedly was replacing them with Amin's Khalq supporters. About 200 were arrested immediately after the coup, and as many as 1,500 may have been sent to jail by last week, diplomats reported.

Diplomatic sources here say they believe that further purges are inevitable as the Soviets try to reshape Army and People's Democratic Party cadres to prop up the new government. Public animosity toward the country's new rulers is strong because of the Soviet invasion that imposed them.

Many of the latest prisoners to be released said they did not know why they had been jailed in the first place. The government has been portraying all political prisoners as the victims of Amin's brutal rule, during which thousands of Afghans suspected of opposition to the government were jailed, tortured or killed.

However, many of those freed apparently were imprisoned before Amin's four-month rule, under the government of Taraki, who now is being billed as a martyr by the Karmal leadership.

Reporters who visited the prison at the government's invitation said it was guarded by some Soviet soldiers. Soviet troops also dominate an access road to the prison and have dug gun positions nearby on a ridge overlooking the main highway into Kabul.

It was not known how many political prisoners were still being held, or why or when they were jailed.

Those released told of the horrors of Policharki, including various kinds of tortures employed under the Amin and Taraki governments.

One Afghan said a just-released brother-in-law had suffered cigarette burns all over his body and electric shock to his face and genitals.

According to Amnesty International, "at least 4,000 and perhaps many more political prisoners," including prominent Moslem religious leaders and holdovers from the previous government of nonaligned president Mohammed Daoud, were being held when an Amnesty delegation visited Afghanistan in October 1978. Since then, the London-based human rights organization said, "Thousands of political arrests have been reported." r

In some cases, Amnesty said, "Whole families of political prisoners were arrested, including women and children."

However, the new government has ignored the Taraki government's role in mass political arrests as it tries to paper out the differences between the Parcham and Khalq wings of the Afghan communist People's Democratic Party and focus the public's widespread opposition on the slain Amin.

Meanwhile, news services reported these developments.

All major cities and highways in the country are in the hands of Soviet forces, although Moslem guerrillas are still able to mount nightime hit-and-run attacks, Western diplomatic sources said.

Diplomats said the Soviets are concentrating their offensive on the mountainous provinces of Badakhshan and Pakitia on the Pakistan border, where they are meeting only isolated resistance.

A rebel radio broadcast Sunday said the guerrillas battling communist rule for nearly 20 months suffered heavy casualties in fighting near the eastern town of Jalalabad, which Soviet troops occupied last week.

The rebel broadcast vowed a "fight to the finish" to drive the Soviets out of Afghanistan and bring down the communist government in Kabul. It claimed the insurgents had been reinforced by "considerable" numbers of Afghan Army troops who deserted during fighting elsewhere in the country following the coup.

Diplomatic sources in Islamabad, Pakistan, reported fighting was also continuing in Parwan, 50 miles northwest of the capital in Kandahar, 270 miles southwest of Kabul, and around Herat, the chief city in western Afghanistan 75 miles from the Iranian border.