Investors who steer clear of Japanese debt do so at their own peril. So say bond aficionados such as Tomoya Masanao of Pacific Investment Management Co. (Pimco), which runs the world’s largest bond fund. The Tokyo-based Masanao goes so far as to say “there is a huge risk not holding bonds.”

Yet the balance of risks may be shifting in the other direction. Why? Obamanomics is heading Japan’s way.

Prime Minister Taro Aso, facing the likelihood of disastrous national elections next month, is increasingly turning to pork-barrel spending, much as President Barack Obama has in the US. It’s Aso’s only hope of winning voters who have given up on his ruling Liberal Democratic Party. More spending means more Japanese debt issuance and higher yields. It could just be that the real “huge risk” is owning too many Japanese bonds.

Aso’s package includes 12.4 billion yen to get rid of fishing gear dumped by foreign boats and 400 million yen for cutting down trees to keep “beasts and birds” out of towns. Oh yes, that’ll help jump-start an export-driven economy.

My problem isn’t with the size of Obama’s $787 billion package – it’s with the paucity of safeguards to keep money from being used in ways that won’t boost demand. Obamanomics as a policy is one thing; its execution is quite another.

What’s more, the odds of additional US stimulus efforts are growing with each disappointing economic report. Ditto for Japan, regardless of the spin we are getting from Aso’s wildly unpopular government. It’s quite a coincidence that the Cabinet Office the other day said the economy is “picking up” – the same week Aso called elections for August 30.

Talk about cherry-picking the few data releases that don’t point to a deeper recession. Indicators also don’t suggest China’s 6% growth is filling the void left by a $14 trillion US economy that remains on its back. It’s here where Obama’s influence comes in. The US President’s massive stimulus efforts are maddening conservatives. They also are giving leaders such as Aso political cover to open the fiscal floodgates. He can always say, “Look at the US” or “Japan needs to do its part.”

In Japan’s case, that will exact a bigger price than in most developed economies.

Junichiro Koizumi can’t be happy. The former prime minister set goals to curtail the world’s largest debt burden and cut public-works projects by as much as 3%. Three prime ministers later, Japan’s debt issuance-machine is back in business. The trouble is, financing fresh spending will get harder as bond yields rise.

Granted, 10-year rates are just 1.3%, close to a three-month low, and a modest increase may be manageable. A big one would suck up funds that Japan needs to prepare for its rapidly aging population to increase competitiveness. It would complicate the Bank of Japan’s effort to normalize interest rates that have been near zero for a decade.

Japan’s ability to maintain order in its bond market will grow trickier. The problem is the so-called crowding-out dynamic that one has to expect as virtually every nation cranks out new debt. With credit markets frozen, policy makers are relying on fiscal pump-priming.

Pundits obsessing over the US becoming Japan-like should consider how the opposite may be true. Japan must make sure it gets more bang for its yen from any additional spending than the US is getting. The US alone will be dropping trillions of dollars of debt on markets. The question isn’t just how efficiently it will be done. It’s also whether there will be enough demand to catch it. Perhaps, and you can bet Obama and Treasury Secretary Timothy Geithner are praying people such as Bill Gross, Pimco’s co-chief investment officer, will show up at auction time.

You can imagine the lobbying campaign in Washington. Keeping China and Japan from dumping their hundreds of billions of dollars of Treasuries is clearly Job No. 1. Keeping investors such as Gross happy also has to be a priority. The same goes for Japan, since demand for debt is finite in a world of seemingly infinite issuance.

Japan has long benefited from a clubby relationship with bond buyers. More than 90% of government bonds are held domestically. They are the main financial asset held by banks, insurance companies, pension funds and households. Really, it’s in nobody’s interest to see Japanese yields rise given the effect it would have on the broader economy.

Only time will tell if Japan can maintain control as it issues ever more debt. The prevalence of Obamanomics will make that much harder and Japanese yields may be headed higher.