Budweiser, the most popular beer brand in America, is kicking off a massive promotional push with a nationwide giveaway of 500,000 free samples in US bars, pubs and restaurants in an effort to shore up an alarming erosion in sales.

Owned by the Belgian multinational Anheuser-Busch InBev, Budweiser is struggling to attract younger drinkers who prefer low-calorie light beers or more exotically flavoured craft beers. Sales were down 9.5% last year, according to the trade publisher Beer Marketer's Insights, the brand's steepest decline on record.

Anxious to reinvigorate demand, Anheuser has declared a "Budweiser National Happy Hour" for this Wednesday and is planning to give away half a million servings by mid-October.

"This is just the beginning," said Benj Steinman, president of Beer Marketer's Insights. "Anheuser-Busch InBev is very, very serious – it's determined to get this brand back on track because of its international importance. But it's going to be a tough battle."

While Budweiser is doing well outside the US, its home market appears to have tired of the red bottle, sharp fizzy taste and sports-focused advertising with slogans such as "Whassup?".

In its half-year results last month, Anheuser-Busch InBev said Budweiser had fared well in Britain, aided by World Cup tie-ins, and was entering promising new markets including Russia. But the company admitted that it was "not pleased" with its overall market share performance, revealing that global volumes were "essentially flat" and that it was "taking steps to stabilise Budweiser sales in the United States home market".

The local newspaper of Budweiser's home town, the St Louis Post-Dispatch, recently noted the "disturbing implications" of a slide in the beer's popularity from a peak US market share of 26% in 1988 to 9.3% last year.

Worries about the brand's long-term decline come two years after Anheuser was taken over by InBev, the brewer of Stella Artois, in a $52bn (then £26bn) deal that sparked anxiety and opposition in the American midwest.

Budweiser dates from 1876, when a German immigrant, Adolphus Busch, decided to try a Bavarian-style lager on American palates. The beer was brewed alcohol-free in the Prohibition and for years has been a default option in US bars alongside brands such as Coors and Miller.

However, Tom Pirko, founder of the industry consultancy Bevmark, believes Budweiser is struggling against a broader variety of competitors: "They can't hold up to the craft beers sector. Americans are pretty tired of what they find to be a 'boiled down' beverage taste."

He said Anheuser may need to radically revamp the beer's image to attract a younger generation: "I think we could see a resurgence and rebirth of the Bud brand and the magic could be put back in the bottle but it's going to be hard, expensive and risky."