There has been a resurgence in terrorist activity in Istanbul, Turkey's biggest city, in the past five days, raising questions about the military government's success in breaking the back of terrorist organizations.

Col. Cezmi Olcay, the man in charge of security in Istanbul's electricity and transport authority, was shot and wounded by two gunmen in Istanbul today during the morning rush hour as he was driving to work. The terrorists escaped.

Last Friday terrorists shot and killed the deputy police chief of Istanbul and his bodyguard. His second bodyguard and driver were gravely wounded. The following day a retired colonel was shot dead while he was playing cards in an Istanbul coffee shop.

The authorities believe that all three attacks were carried out by extreme left-wing gangs.

To many Turks the bloodshed was an uncomfortable reminder of the period before last September's military takeover when Turkey seemed on the verge of civil war. Dozens died in terrorist incidents every month until Gen. Kenan Evren, the chief of staff, and other military officers overthrew the civilian government and moved against political terrorism.

The military declared martial law throughout the country and cracked down severely. There are now nearly 21,000 left- and right-wing political prisoners. About 100 alleged terrorists have been killed as the Army broke up many terrorist organizations. Terrorist acts were down by nearly 90 percent, according to official figures.

Nevertheless, the government seems to realize that it is not yet in a position to proclaim complete victory. "The threat we are facing is of such enormity that there is no possibility of relaxing martial law in the immediate future," a senior official said yesterday.

It is too early to assess the implications of the acts of terror in Istanbul. The authorities have not made their views public. Some observers consider the attacks to be the last spasms of armed gangs mauled by the military, designed to boost morale among their supporters. Others speculate that terrorists may have regrouped after the shock of the military's initial offensive and may be making a comeback.

Whatever the case may be, there is no doubt that the shootings constitute acts of defiance that the Army will not ignore. Three of last week's alleged assassins have already been identified and security has been noticeably tightened in Istanbul as a manhunt was organized to catch them.