(Recasts; adds details on tender)

CARACAS/HOUSTON, Dec 6 (Reuters) - Venezuela’s largest refineries were operating below half capacity this week, prompting state-run oil company PDVSA to launch tenders for product imports amid the OPEC country’s deteriorating infrastructure and ebbing crude production.

The country’s massive 955,000-barrel-per-day Paraguana Refining Center was operating at around 45 percent of capacity on Monday, according to an internal PDVSA document seen by Reuters on Tuesday, a poor showing that is likely to signal further need for product imports.

The 645,000-bpd Amuay refinery was running at about 308,000 bpd, while the adjacent 310,000-bpd Cardon facility was at 118,500 bpd, according to the document.

PDVSA this week launched an offer to buy two 300,000-barrel cargoes of gasoline blend stock and a 300,000 barrel cargo of high-sulfur diesel for December delivery, traders said on Tuesday, increasing expected imports for the last quarter.

The company has since November requested some 3.3 million barrels of gasoline and diesel on the open market for prompt delivery.

Even though supplying firms have recently faced long waiting times to discharge cargoes at Venezuelan ports due to payment delays, PDVSA this month also launched tenders to buy up to 6 million barrels of heavy naphtha for 2017 and 1.65 million barrels of U.S. crude, with deliveries starting in December.

Venezuela’s refineries have been plagued with blackouts, equipment issues and stoppages for years.

PDVSA often blames problems on “saboteurs” intent on bringing down socialist rule in Venezuela, and says its foes and hostile media try to exaggerate refinery issues. Critics say years of underinvestment and poor maintenance are the cause.

The Caracas-based company did not respond to a request for information on the refineries.

The refinery segment is on course for its poorest showing in years, perhaps even lower than in 2012, when a massive fire at Amuay killed over 40 people and dragged Venezuela’s refining operations down to around a half their 1.3 million bpd capacity.

Worsening the situation, Venezuela’s two smaller refineries, with capacities of 146,000 barrels per day and 187,000 bpd respectively, have barely been refining crude in the last few weeks, according to union sources and workers.

PDVSA has been trying to restart Puerto La Cruz since Monday night, according to a worker, but attempts to get two crude distillation units and the catalytic cracker going have failed, he added, and fumes were spilling out of the complex.

“The order is to get the refinery going no matter what, but it looks like God’s own hand is not letting the units operate in these bad conditions,” the worker said.

As crime continues to hit Venezuela’s oil industry, an internal pipe that sends gasoline to the Yagua sorting stations in Carabobo state was stolen last week, a worker said. Oil Minister Eulogio Del Pino on Tuesday said there had been “sabotage” in Yagua.

To compensate for the refining problems, PDVSA imported an average of 63,000 bpd of refined products from the United States during the three first quarters of this year.

Since August, its U.S. unit Citgo Petroleum has been sending three to four monthly cargoes of diesel, gasoline blend stock and jet fuel to its parent company, according to sources and Reuters data. (Additional reporting by Mircely Guanipa in Punto Fijo; Editing by Jonathan Oatis and Dan Grebler)