WASHINGTON — President Bush on Wednesday signed into law the first major changes in postal operations in decades, offering hope for reducing or delaying future rate increases. For now, people will not notice anything different at the post office.

“This is a historic accomplishment and will help one of the most revered institutions in America survive and prosper in the electronic age,” said Rep. Henry Waxman, D-Calif.

Sen. Susan Collins said the changes are the only way to avoid what congressional investigators referred to as a “death spiral” — excessive and unpredictable rate increases that result in a lower volume of mail.

Collins, R-Maine, noted that the Postal Service is the linchpin of a $900 billion mailing industry, providing 9 million jobs in fields such as direct mailing, printing, catalog companies, paper manufacturing and financial services.

Postmaster General John E. Potter said the law could not have come at a better time. “The Postal Service has never been stronger, and this law enables us to build on our successes,” he said.

In an important change, the law shifts responsibility for some retirement benefits to the Treasury.

Many postal workers once served in the military. Unlike other federal agencies, the post office had to pay for retirement benefits earned during both the military and postal careers of those workers.

Benefits earned during military service will be charged to Treasury now, relieving the post office of having to pay billions of dollars in the future.