The government and army certainly made serious efforts to supply Leningrad. The last railway line into Leningrad was cut at the end of August 1941, and the last land routes (i.e., roads) were cut about a week into September. Supply shifted to boats and small ships on Lake Ladoga, and also air. Food and military supplies went in, and industrial equipment and expert personnel and ammunition (manufactured in Leningrad) went out. Two Soviet offensive were launched in order to re-open the land supply routes, in mid-September and again in late October. Both failed.

Alas for these efforts, a German offensives cut the railway line from Moscow to Lake Ladoga on 8th October, which seriously reduced the ability to supply Leningrad over the lake. The Soviet response was a counter-offensive which began 4 days later. This re-opened the railway to Lake Ladoga, but failed to recover any of the land routes into Leningrad. This offensive ground to a halt in late December.

November and December were when Leningrad largely ran out of food and supplies. Adequate supply was not possible in this time, since (a) a serious supply effort takes time to gather the transport, improve roads and railways, etc., and (b) the temporary closure of the railway to Lake Ladoga was a huge problem for supply. The events of November and December are worth looking at in more detail.

The failure of the first Soviet counteroffensives convinced the Soviets that the land routes might stay closed for a long time, and supplying Leningrad would be a big problem. Thus, as soon as the ice on Lake Ladoga become strong enough, work began on ice roads over the lake. The thickness of the ice limited the building of the ice road at first, but expansion and improvement continued until the thaw in spring. The first supplies via the ice road came into Leningrad on the 19th of November, but the amount moved in the first few days was small, since the ice was not yet thick enough for trucks (horse-drawn sleds were used). From 22nd November, supplies were reaching Leningrad by truck. At this point in time, the Moscow-Ladoga railway line was still cut, and trucks had to be used to move supplies around the limit of the German advance. Warmer weather at the end of November resulted in a partial thaw, and reduced ice road capacity.

It was at this point that the Soviets made a mistake, with serious consequences for Leningrad. The supply effort over the ice roads was resulting in serious losses of trucks - parts of the route were within German artillery range, and the Germans used their artillery to try to (unsuccessfully) stop the traffic. German air attacks threatened the entire ice road, and on some days, air attacks were carried out all day. This, combined with the expectation that the ongoing offensive (prompted by the Germans cutting the Moscow-Ladoga railway line), which was pushing the Germans back, would re-open land routes into Leningrad, led the Soviets to first reduce the ice road traffic, and on 12th December to suspend the supply operation. A mistake, but not a bone-headed mistake, and certainly not a deliberate attempt to starve Leningrad. However, this suspension could easily be spun into a claim of deliberate undersupply. When it was realised that the offensive was not going to re-open land routes, supply over the ice road recommenced (later in December). Even then, the condition of the ice still limited traffic until the end of December.

Once the railway line was back in Soviet hands and repaired, the situation improved. The railway line was extended all the way to the lake, further reducing the need for trucks - this extension took from mid-January to the end of February, so the resulting improvement in supply was only in March and April. The improvement was significant: about double the amount of food and other supplies was delivered in March, compared to January. January had seen much more supplies delivered than November and December.

Still, Leningrad had run out of food and fuel by the end of December, and January and February 1942 were the peak of the famine. In February, the deaths due to starvation dropped, and largely stopped in March, and supplies were built up and successfully lasted through the period when the thaw stopped traffic on the ice road (in April) but the ice on the lake still stopped shipping on the water. Supply was helped by the evacuation of perhaps 1-1.5 million people from Leningrad over the lake. Industrial equipment, including railway cars continued to be removed from Leningrad, but the capacity of the routes allowed an official evacuation program in mid-January (there had been earlier unofficial evacuation, with many deaths from German artillery and air attack, and the weather).

After that first winter, supply was essentially adequate, and the mass starvation of the winter of 1941-1942 was avoided. As the winter of 1942-1943 approached, the Soviets were much better prepared. As far as transport over the ice was concerned, the weather was much worse (i.e., it was warmer), and the lack of thickness of the ice limited the capacity of the ice roads. Still, supplies were moved without the early difficulties of the previous winter. Construction of a railway over the ice began (which would have greatly increased the supply capacity if completed), but was abandoned when the Soviets recaptured a land corridor into Leningrad.

In summary, the greatest difficulty was early in the siege. The Soviets were unprepared to supply Leningrad after the overland railway and road routes were cut by the Germans, and it took time to make the alternative routes over Lake Ladoga effective. In hindsight, the decision to suspend the over-the-ice supply operation in December was a mistake, but in the absence of hindsight, it would appear a rational decision. The Soviet sin in that decision was overoptimism about the future progress of their ongoing offensive to open supply routes (which re-opened the Moscow-Ladoga railway, but not the land routes into Leningrad), rather than deliberate starvation of Leningrad. The steady improvement in the supply situation shows that there was a serious intent to properly supply the city, but there was great suffering before the supplies were flowing adequately.