The Soviet Union's massive Christmas week invasion of Afghanistan was a swift , well-oiled operation, planned methodically with Moscow's Warsaw Pact allies. This is the conclusion of senior US intelligence analysts who now seek to determine "where the Soviets go from here," as one Pentagon expert put it.
Urgency is added to their question by the realization here that not all of the Soviet moves were successfully tracked by Western intelligence. Some analysts are wondering whether present Soviet combat operations against the Afghan Muslim insurgents may not partly screen from view new Soviet preparations for further moves.
Such moves might include "hot pursuit" of Afghan rebel units to their bases inside Pakistan -- which President Carter has said would trigger the 1959 US-Pakistani defense treaty -- or even eventual moves across the border between Soviet and Iranian Azerbaidzhan, in Iran's northwest, where Turkish- speaking Azeri militants oppose Ayatollah Ruhollah Khomeini's Persian- speaking government.
US Defense Department experts, suspecting Soviet deception tactics, have been rereading passages like this one from a Soviet military commentator, Maj. M. A. Ziyeminsh, in Red Star, the Soviet army newspaper, published a year ago:
"It must be said how important it is to conceal one's true intentions, manpower and equipment, and combat resources from the enemy. Frequently, in order to achieve this and lead the enemy into a mistake, something more is required than just clever camouflage. . . . It is necessary, for example, to use military cunning, sometimes even on a very large scale."
Nearly 40,000 Soviet combat troops (including the original 3,500 Soviet military "advisers" assigned to the overthrown regime of the late President Hafizullah Amin) have crossed the northern frontier or have been airlifted to Bagrame air base, north of Kabul or directly to Kabul, since Dec. 19.
By Jan. 3, fighting between the Soviets and the Afghans was in progress in mountains near Paghman, just west of Kabul and south of Herat, which is in western Iran. Eyewitnesses in Iran reported arrival of thousands of Afghan refugees from the fighting.
In the Hindu Kush mountain finger of northeast Afghanistan pointing at China, Soviet forces reportedly fought rebels along the single mountain road leading to the 50-mile- long border with China, near the junction of the Chinese, Pakistan, and Soviet frontiers.
Other Soviet units then fanned out to provincial capitals. Some were reported fighting Muslim rebels as well as some afghan army units which apparently had refused Soviet orders to surrender their arms. Earlier, diplomatic reports from Kabul said the Soviets had disarmed the remnants of the first corps of the formerly 90,000-man Afghan army. In Konarha Province, bordering Pakistan, the Afghan commander has refused to obey Soviet orders and has halted operations against the rebels.
One Soviet motorized rifle division of 12,500 men has deployed along the main north-south road in Afghanistan's far west, between the Soviet border base of Kushka and the provincial Afghan capital of Herat. There they command a main highway link into Iran, on the highway to the northeastern Iranian city of Mashad, a place equally holy to Iranian Shia Muslims as Ayatollah Ruhollah Khomeini's stronghold of Qom, south of Tehran. Other Soviet troops advanced Jan. 3 southeastward from Herat toward Kandahar.
However, for Pentagon planners, the obvious Soviet threat to Iran is perhaps less urgent a problem than Soviet access to Afghan air bases, such as Kandahar, and Shindand, just south of Herat.
This puts the Soviets within less than 500- mile air-strike range of the Hormuz strait, the crucial choke-point entrance to the Gulf's oil fields and ports where the industrial world loads the majority of its oil imports. They are also now within easy surveillance and striking distance of the 20-ship US naval force, including two carrier battle groups, in the nearby Arabian Sea.
Six crack Soviet airborne battalions are already in place at airfields near Kabul with their transport planes and helicopters.
"This means," a US Navy source explained, "quite simply that Soviet aviation -- whether tactical or long-range -- no longer needs to fly the 1,000 miles or so from the Soviet base at Aden (in South Yemen), or to overfly Iran and Pakistan from the USSR in order to get at our forces in the Indian Ocean."
As the Iranian crisis broke with seizure of the US Embassy in Tehran Nov. 4, Soviet preparations for the advance into Afghanistan already had begun. Warsaw Pact forces in East Germany, Hungary, Czechoslovakia, and Bulgaria were alerted.
So much notice was taken in East Europe of the alert, and of the start of recall of Soviet and East German reservists, that East German Prime Minister Willi Stoph felt it necessary to publicly deny that there was an alert because of Iran.
After talks in Aden with the Marxist South Yemen government, Mr. Stoph and the East German defense minister flew to Moscow in early December. They met with top Soviet brass, including the Warsaw Pact commander in chief, Gen. A. I. Gribkov and the ground forces commander, Gen. Ivan Pavlovsky, who had earlier surveyed Afghanistan with a 50-man Soviet team of experts.
Also present were Warsaw Pact liaison officers and commanders of the Soviet Union's Turkestan and Transcaucasus military districts (bordering Afghanistan, Iran, and Turkey).
At least three divisions then moved to bases like Dushanbe, capital of Soviet Tadzhikistan and border stations like Termez, where General Pavlovsky now directs operations, and Kushka. Some Western analysts believed one object was to protect the big Soviet natural-gas pipeline that carries a large proportion of the southern USSR's energy needs from Afghanistan, as does a similar pipe from Iran.
Certain Soviet units were airlifted all the way from East Germany and Hungary. Some East German backup forces moved by rail into more advanced bases in Hungary and Bulgaria. Civilian airline flights were requisitioned to carry troops and supplies. Western military attaches in Moscow were prevented from getting a look at preparations by travel bans.
Many Soviet units contain "ethnic" Persian, Uzbek, or Tadzhik-speaking troops and officers. Some of them can communicate with some Afghans in their own languages.