BENTONVILLE, ARK. ? Wal-Mart Stores Inc., under attack for its health care coverage for its employees, plans improvements that would include expanding the availability of its lowest cost plan and shortening the waiting periods to enroll part-time workers and their children.

At the same time, Wal-Mart Chief Executive Lee Scott said Thursday that employers cannot continue to meet the rising costs of health care and urged a government-business partnership to find an answer.

The announcement marks the second time in six months that the world’s largest retailer has moved to improve health benefits and comes ahead of Scott’s speech Sunday about the issue to the nation’s governors, who are looking for ways to cap rising costs for taxpayer-funded health plans that cover the uninsured.

Scott also is expected to renew Wal-Mart’s criticism of bills filed in at least 22 states – including Kansas – that would force the retailer to spend more on health care.

Wake Up Wal-Mart, one of Wal-Mart’s harshest critics, called the retailer’s attempts to improve its health care plan as “nothing more than a facade.”

“Wal-Mart’s proposed changes are clearly designed to try and salvage a faltering public image, rather than make substantial changes to improve health care benefits for its employees,” said Paul Blank, campaign director for Wake Up Wal-Mart.