More than 3,000 political prisoners have been executed and many thousands more locked up in overcrowded prisons by the shaky revolutionary regime in Afghanistan, according to reports reaching U.S. officials.

The reports depict regular executions, estimated at 20 to 50 a night, at Pol-I-Charki prison outside Kabul, capital of the remote, mountainous country. Victims of the imprisonment and executions, according to the reports, are military personnel, religious leaders, major figures in previous governments, large land owners and a variety of others considered hostile to the rulers.

"We are deeply concerned about the situation," said Assistant Secretary of State Patt Derian, who heads the State Department's human rights activities. "The human rights situation in Afghanistan is not widely known, but we are receiving continuing reports of mass arrests and executions."

A leftiest government headed by Nur Mohammed Taraki, a former press attache in the embassy in Washington, took power in a coup in April 1978. The new regime quarreled with traditional leaders and with many tribal groups, conducted internal purges against factions of the small revolutionary party, and turned increasingly for support to the Soviet Union.

American officials estimate that the ruling regime now controls less than half the country and much of that only in daylight hours. A variety of insurgent groups, including tribal units based in neigboring Pakistan, are reported taking a heavy roll of embattled government forces.

American officials believe the Taraki government is under subtle or overt pressure from trhe Soviets to broaden the regime rather than risk collapse in the deepening insurgency. With the past several weeks Soviet news media have begun speaking of an Media have begun speaking of an Afghan "united front," though none is visible to other observers.

Soviet pilots have been reported flying helicopters and transport aircraft, but there is no indication that the Taraki regime has turned to the Russians for combat or occupation troops. Such an action would be a desperation move with uncertain consequences among the independent-minded Afghans, according to American observers.

Many prominent Afghans reportedly were executed shortly after last year's coup. Roundups of opponents and executions are reported to have continued as the regime faced growing conflict with broad segments of Afghan society. According to the reports reaching American officials:

Some 390 religious and business leaders from Kandahar Province were taken to Pol-I-Charki prison last October after uprisings in that area. They were blindfolded, their watches and money removed, then beaten and executed by firing squads 10 at a time. Their bodies were thrown into a common grave and bulldozed.

Two busloads of condemned military offices overpowered their guards on the way to the execution site two months ago. More than 80 persons were killed in the ensuing battle, which spread into the prison and was suppressed by government troops. Some of the prisoners escaped.

Pol-I-Charki prison, originally built for no more than 6,000 persons, is overflowing with about 15,000. Prioners sleep on a rotation system.

Among the few positive signs are recent reports that around 70 members of the Parcham party, one of two original factions of the ruling regime, have been released from prison. A number of Parchamite leaders, who were intially posted as ambassadors after the revolution, have taken refuge in East European countries.

The United States has cut off all new aid to Afghanistan, withdrawn the Peace Corps and reduced official personnel, especially after the killing of U.S. Ambassador Adolph Dubs in Kabul last Feb. 14. The United States recently voted against several loans for Afghanistan in international financial agencies and made high-level presentations in Kabul about human rights abuses.