WASHINGTON (AP) — The cost of mailing a letter goes up a penny to 42 cents on today, the latest in what are expected to be annual price adjustments by the Postal Service.

A new law regulating the post office makes it easier to raise rates as long as the agency doesn’t exceed the rate of inflation. Rates are to be adjusted each May.

But the post office also has introduced a way for people to save money when the price goes up, the Forever stamp, which remains valid for first-class postage regardless of any increases.

With the rate increase approaching, sales of the Forever stamp reached 64 million-a-day in April, postal officials said.

Forever stamps currently sell for 41-cents, but can be used after the rate increase without any additional postage. However, when the rate goes up, so does the price of Forever stamps.

Unlike the Forever stamps, other 41-cent stamps will require additional postage under the new rates, and postal officials said they printed an additional 1.5 billion 1-cent stamps in anticipation of the demand.

Also, for the first time the agency has stamps available at the new rate before the change takes effect.

A set of five 42-cent stamps honoring pioneering journalists went on sale in April, as did a set of four stamps featuring the American flag flying at different times of day.

A 42-cent stamp featuring singer and actor Frank Sinatra will be released Tuesday.

The increase comes just a week after the post office announced it had a loss of $700 million in the second quarter of the fiscal year, blamed largely on declining mail volume and rising fuel prices.

While the charge for the first ounce of a first-class letter rises to 42 cents, the price of each added ounce will remain 17 cents, so a two-ounce letter will go up a penny to 59 cents.

The cost to mail a post card will also go up a penny, to 27 cents.

Other rates set for Today:

— Large envelope, 2 ounces, $1, up 3 cents.

— Money Orders up to $500, $1.05, unchanged.

— Certified mail, $2.70, up 5 cents.

— First-class international letter to Canada or Mexico, 72 cents, up 3 cents.

— First-class international letter to other countries, 94 cents, up 4 cents.

— Priority mail flat-rate envelope, $4.75, up 25 cents.

— Express mail flat-rate envelope, $16.50, up 25 cents.

But, the Postal Service said that overall prices for Express Mail, its overnight service, will be lower at the weights and in the delivery zones used by most customers.

And Express mail and Priority mail customers can save money simply buying postage online, the agency said. Express mail customers will receive 3 percent off the published retail prices and Priority mail customers will save an average 3.5 percent.

In Los Angeles, Stamps.com said it has released new software which will include discounts on Express and Priority mail for customers buying postage through its Internet site, targeted to small business and home offices.

Postage rates last went up in May 2007, with a first-class stamp jumping 2 cents to the current 41-cent rate. That change came under the old law governing the post office, while the current boost uses the simpler procedures of the new one.