Exxon Corp., under prodding from the Bush administration, announced Wednesday it plans to sharply increase the number of workers and ships cleaning spilled oil from more than 300 miles of Alaska shoreline.

Transportation Secretary Samuel Skinner applauded the move and said it improves the likelihood that the oil company will meet its cleanup goals for this summer.Nevertheless, the cleanup effort might still have to be continued in the spring of 1990, Skinner said. Exxon said it is confident it can clean the shoreline by September with the added manpower and ships.

The tanker Exxon Valdez ran aground in Alaska's Prince William Sound on March 24, spilling nearly 11 million gallons into the pristine waters of the sound. Within days the oil spread down the southern Alaska coast causing environmental and economic havoc.

The Coast Guard estimates that more than 300 miles of rocky shoreline needs to be cleaned by hand and high-powered water hoses. In recent weeks, cleanup efforts have proven to be much more difficult than Exxon had expected.

In a revised cleanup plan submitted to the Coast Guard, Exxon said it will increase the number of people to be involved in the summer cleanup from a previously planned 3,400 workers to 5,000. It also said it will bring in seven additional barges and 17 more landing craft, bringing the number of vessels to 70.

The additional manpower and vessels "will allow the number of people directly employed on the battlefront - on the shoreline - to increase by over 1,000 from 1,475 to 2,500," William D. Stevens, president of Exxon Co. U.S.A. said.

In other developments Tuesday:

-A 50-foot landing craft involved in the cleanup sank in Valdez Arm. The three people aboard the vessel Hummer were rescued uninjured, the Coast Guard said.

-The high-tech Soviet skimmer Vaidogubsky was being sent home after Exxon declined to renew its $15,000-a-day contract. The ship had been skimming oil for a month, but its pumps and machinery jammed frequently on the thick, weather-hardened crude.

"We shouldn't blame the Russians," Exxon operations manager Bill Rainey said. "It was just not the type of oil she was good in."

-In Washington, a bill that would require oil companies to be able to handle spills within five hours was introduced in the House.

-Authorities extended by five days the deadline for having the worst oil damage cleaned off four islands in Prince William Sound, a favorite birthing area for seals. The new deadline is May 15.

Exxon and the federal government has been under sharp criticism for its lack of coordination and pace of the cleanup in the first few weeks after the spill. Since then, the Coast Guard gradually has assumed increased oversight in the effort, although the actual work and development of cleanup plans continue largely to be in Exxon hands.