The shah of Iran has belatedly recognized that the biggest single weakness in his defenses is the lack of trained troops and equipment to control civilian riots without resorting to violence, Carter administration officials said yesterday.

The shah recently conceded to American embassy officials in Tehran that in ordering $20 billion worth of the latest U.S. weaponry he overlooked the need for riot-control forces and now is making a crash effort to make up for lost time.

Before the rioting got so out of hand that the shah had to resort to martial law, the administration was so concerned about Iran's need for crowd control training that it was prepared to send U.S. Army troops to Iran to train its troops in handling crowds without harming them.

U.S. officials disclosed that training proposal, which was not implemented, in asserting yesterday that their concern dated back several months when demonstrations in Iran were comparatively easy to handle.

The shah told U.S. officials recently that he plans to embark on a crash effort to train his troops in using tear gas and clubs rather than guns and live bullets to control demonstrators in his country. U.S. police and troops used the less violent methods during the Vietnam protests.

While the shah moves to combat the threat he failed to anticipate, he is telling U.S. officials to delay preparing any new orders for him to sign for additional planes, ships or armor.

However, Pentagon officials said yesterday, the shah has made no sign that he intends to cancel the $11.56 billion in weapons already on order but not yet delivered. Included in that category are seven airborne warning and control system (AWACS) planes for $1.2 billion and 160 F16 fighters for $3.2 billion.

Beyond those weapons considered firm orders at the moment, although the shah could end up canceling them if the situation worsen in Iran, there have been discussions of buying additional U.S. weaponry, including 70 more Grumman F14 fighters and 140 more General Dynamics F16 aircraft.

The additional F14s and F16s are on that new shopping list that has been ahoved aside as the shah concentrates on the domestic crisis.

The long-range relationship between the U.S. government and its biggest overseas customer for modern weapons is thus clouded by the unrest in Iran. The shah's awesome arsenal designed to combat external threats is proving of little use to him for the internal one. The Pentagon said that the shah has ordered a total of $19.38 billion in modern planes, missiles, armor and ships.

President Nixon back in 1972 told the shah that the United States would sell him modern weapons, including the sophisticated F14 fighter armed with Phoenix air-to-air missiles. The Nixon administration saw arm sales to the shah as one way of offsetting the cost of importing oil.

Pentagon figures show this pattern of military orders and deliveries to the shah since fiscal 1972: