After the failure of a much-heralded counteroffensive and another winter of fending off Russian attacks, Ukrainian troops are exhausted and facing severe shortages.

The government has signed off on a conscription plan to replenish the ranks, and European countries have promised to send more vehicles and missiles, among other critically needed supplies. Ukraine received a much-needed boost on Saturday, when the U.S. House of Representatives approved a $60 billion military assistance package that will provide more weapons to their war effort.

But what Ukraine really needs is time.

Training those new troops will take months, and the European equipment will arrive gradually, over the course of the year.

Analysts believe that Ukraine is unlikely to start a major counteroffensive this year, choosing instead to spend the time reconstituting its forces. But it will still need to try to stave off Russian attacks and to keep any small enemy gains from becoming full-fledged breakthroughs.

That is where the ambitious defensive lines that are frantically being built come in.

The Ukrainian government has allocated about $800 million to building fortifications along about 600 miles of front line this year, and construction is well underway.

The defenses shown above are just a small part of what Ukraine has been putting in place, much of which can be seen in publicly available satellite imagery from Copernicus, part of the European Union’s space program.

American military analysts in Wiesbaden, Germany, drawing on satellite imagery and other intelligence, have been working closely with Ukrainian liaison officers to identify gaps in Ukraine’s defenses, officials say.

Since the start of the year, Ukraine has built long defensive lines across two regions in the south, Kherson and Zaporizhzhia.

As well as the new defenses in the south, Pentagon officials and independent analysts also pointed to ones beyond Avdiivka in the east.

The Ukrainian military is eager to prevent a repeat of what happened around Avdiivka in February, after that city was captured by the Russians. Meager Ukrainian defenses allowed the enemy to keep pushing west.

So far, four officials said in interviews, the results have been mixed. A robust, multilayer tiered defense is still weeks away, if not months, they said.

But the top U.S. commander in Europe, Gen. Christopher G. Cavoli, expressed optimism.

“I think that their defenses are going to be very strong, and are strong,” General Cavoli said in a brief interview. “And with continued support, they’re going to be in a good position.”

But on the ground, it has not been easy.

On the outskirts of one embattled town, Chasiv Yar, exhausted troops are holding onto terrain around a canal. But their defenses are poorly constructed and should have been fortified with concrete months ago, a Ukrainian commander said.

Now the Russians are close to fighting street to street.

The defenses going up in eastern Ukraine are markedly different from many of those in the south. In place of broad defensive lines are installations meant to fortify urban areas that are in Russia’s sights.

One of them is Kurakhove.

The city lies on a main road 10 miles northeast of Marinka, which Russia began trying to capture in 2014, when it was making incursions into Ukrainian territory.

Marinka finally fell late last year. Satellite imagery now shows Ukraine working to protect Kurakhove.

This effort indicates that the Ukrainians are directing their resources to the most defensible terrain, with the idea of making ground advances as costly as possible for Russia.

The defenses also point to a strategy across much of the front line that involves keeping Russian forces off guard with small attacks and seeking to exploit flaws in their defenses, officials said.

For now, with minefields and fortifications making it difficult to attack and maneuver without big losses, both sides are relying heavily on well-prepared entrenchments.

These can include deep trenches fortified with cement, overhead protection, heating and sleeping areas. They require extensive manpower to build and to defend. With Ukraine’s ranks thinned by casualties, it remains unclear if it is up to the task.

James Rands, a military analyst with Janes, a defense intelligence company in London, said the defenses Ukraine built during earlier conflicts with Russia were exceptional. In Donbas, he said, the bunkers were dry and protected with overhead cover, fire-proofing and ballistic protection. The trenches were reinforced.

With Russia now mounting a full invasion, Ukraine is unlikely to be able to do that again, Mr. Rands said.

“The positions they have fallen back to are not in the same league by any stretch of the imagination,” he said. “Ukraine now needs to build a series of defensive positions whilst in contact — which is difficult.”