SAN JOSE — When the new Silicon Valley patent and trademark office was proposed 1½ years ago, it was hailed by politicians and business leaders as a blessing for local entrepreneurs and inventors. But so far, the project seems more like a curse for taxpayers.

With construction set to begin Friday at San Jose City Hall, officials revealed that the total cost of the project is now pegged at $18.2 million, triple the original estimate. And its opening has been delayed — again.

The good news for the city of San Jose is that the federal government is picking up most of the increased portion of the tab. The City Council is set to approve the inflated budget and longer timeline on Tuesday, the second major cost increase and delay to the project in as many years.

The U.S. Patent and Trademark Office chose San Jose for one of four new outposts in late 2013 after four years of lobbying from local leaders. At the time, officials said the cost to retrofit a partly empty portion of the downtown City Hall wing along Fourth Street would be about $6 million. Last year, the cost jumped to more than $10 million when it was revealed that most city employees in the wing would need to be moved across the plaza to the main 18-story City Hall tower, adding significant relocation costs.

Now, with the design completed, it turns out even those higher estimates undershot the price tag.

Barry Ng, the city’s interim public works director, said there were “some very distinct design challenges” to build a specialty office for more than 100 patent examiners and judges, along with space for the public. Even though City Hall is less than a decade old, the majority of the space being used for the patent office is just a shell with only walls, ceilings and floors.

Additionally, the task of relocating city departments is more complicated than first thought, requiring more heavy construction.

“A lot of the costs started to creep in, and creep up,” Ng said.

City officials stress that they still forecast making all their money back in seven years through rent payments from the USPTO leasing 35,200 square feet of space; and if the agency decides to stay longer, the city has a chance to make money off the deal. Local leaders continue to tout the economic benefits of having their first permanent patent and trademark office, an upgrade from the current temporary Menlo Park location or the need to fly to Washington, D.C.

In a brief statement, the USPTO said only that it “had to keep track of shifting real estate pricing, and other market realities, which have impacted the cost and time of setting up our new permanent space.”

The city has allocated $850,000 from higher-than-expected revenues during the economic resurgence to cover its share of the latest cost increase, while the USPTO will fund the rest, though it did not say how. The feds are paying for the actual $12.7 million satellite office while the city is footing the $5.5 million cost to relocate its employees. At the same time, the timeline for the project — delayed during the federal sequester years ago and then again last year — has been pushed back another two months, with an opening now set for October. Ng said the design changes contributed to the late start and said construction will still fit into a “very tight schedule.”

President Barack Obama in 2011 had announced plans for four satellite offices, which had been set for Detroit, Dallas, Denver and somewhere between San Jose and Mountain View. Although it’s unclear if any other local city offered subsidies to get the office, San Jose officials said they kicked in extra money because they were worried about losing the hub to a neighbor.

The City Council, which has previously been united in its support for the patent outpost, is expected to approve the plans on Tuesday after public works officials previously agreed to the added costs. The contractor, Turner Construction, is already set up at the site and has spent weeks preparing for the job.

Contact Mike Rosenberg at 408-920-5705. Follow him at Twitter.com/RosenbergMerc.