SHANGHAI, China — The dull gray hulls of four sleek new fighting ships, bristling with cannons, radar antennas and bulbous electronic pods, bob beside the Huangpu River shipyards where they are in the final stages of construction for the Chinese navy.

Giant military transports float placidly nearby, getting fitted under the supervision of uniformed officers to boost the Chinese military’s ability to move men and materiel across the sea.

Viewed from a Shanghai commuter ferry, these are the outward signs of China’s military modernization program, a campaign to improve what experts count as the world’s largest fighting force, with more than 2 million members. The effort, widely hailed by Chinese leaders, has been underway for years. But it has accelerated markedly since the late 1990s, when then-President Jiang Zemin concluded that China needed a more potent and up-to-date military if it was to compete seriously in the world arena and back up its policy on reuniting Taiwan with the mainland.

For the past 18 months, foreign military experts have observed, the military has concentrated particularly on strengthening its sea power. The main reason, they say, is to provide the government in Beijing with a military option if Taiwan declares independence and brings the long-simmering standoff to a boil.

"These people are building ships like nobody’s business," a military attache in Beijing said.

Construction has begun on about 70 military ships over the last 12 months, including a number of landing craft, and China is considering acquisition of another two Soviet-designed destroyers to complement the three it already owns, he said. More submarines are the subject of negotiations or already purchased, adding to the four bought several years ago.

Although China has an estimated 500 missiles capable of hitting Taiwan, 100 miles off the mainland, foreign officials and military experts say they do not believe the Chinese military has the training to mount an invasion. The newly built or newly purchased ships and equipment have yet to be fitted and manned, a process that takes several years. The Pentagon estimates that China now has the ability to sealift only about one division, or 10,000 men.

But some of these observers have concluded that the rapid shipbuilding program, combined with other acquisitions and training, could provide China’s leaders with a limited military option within several years.