* Two-week tournament seen as dry run for 2018 World Cup
* Will test logistics, security of soccer infrastructure
* Scandal-ridden St Petersburg stadium to be showcased
* Putin has approved tougher penalties for hooliganism
By Mikhail Antonov and Nikolai Isayev
MOSCOW, June 7 (Reuters) - Russia has boosted security and scrambled to finish an $800-million stadium as it banks on the eight-nation Confederations Cup to gauge its readiness to host the World Cup next year.
Russia will showcase four of its 12 World Cup venues, including the scandal-plagued St Petersburg Stadium, in a two-week tournament kicking off June 17 that will feature world champions Germany, the various regional champions and the host country.
Russia, now a record low 63rd in FIFA world rankings, have experienced upheaval with three managers in the last two years. But the country hopes to present itself as an able host in a far-flung tournament that will test the security and logistics of its soccer infrastructure.
The tournament, held in Moscow, St Petersburg, Sochi and Kazan, is also meant to ensure the 2018 World Cup in President Vladimir Putin's Russia runs smoothly as he faces political isolation over the conflicts in Ukraine and Syria.
Since clashes between Russian and English fans tarnished the European championship in France last year, Putin has approved legislation that toughens punishments for violence at sporting events as part of a broader crackdown on hooliganism.
The authorities say the Confederations Cup's ticketing system, which requires ticket holders to apply for a personalised fan-ID, will ensure that fans are screened and hooligans kept away.
"Citizens who have committed gross legal violations during sporting events, demonstrated racism, set off fireworks, broken furniture, tried to start fights, are under our unwinking, constant stare,” Anton Gusev, deputy head of the interior ministry department overseeing security at sports venues, told reporters on Tuesday.
"This also pertains to foreign soccer hooligans."
The ministry has blacklisted 191 fans, including 54 spectators involved in a pitch invasion at the Russia Cup final in Sochi, an incident that revived concerns about the readiness of Russian soccer venues to handle crowds.
A bombing in the St Petersburg metro that left 16 dead in April also sparked fears that a similar attack could hit Russia during the tournament.
Russia's Federal Security Service (FSB) tried to assuage concerns on Tuesday, saying terrorism did not pose a threat to Confederations Cup participants and spectators.
A decree signed by Putin last month sparked outrage among Kremlin critics after it imposed tighter restrictions on public gatherings and limited the use of air space and waterways over a 42-day period covering the Confederations Cup.
The decree also requires that foreigners be registered with Russian authorities within one day of their arrival in the country.
The limits on public gatherings, which will also be in force during the World Cup, mean that all rallies, pickets and protests unrelated to soccer in the host cities' regions can take place only at times and locations approved by the authorities.
Activists have decried the fact these restrictions will be in place during nationwide anti-corruption protests on June 12 called by opposition leader Alexei Navalny, after a first round of demonstrations in March saw thousands take to the streets.
A protester holding a sign that read, "I don't care about soccer, I picket where I want," was detained last week outside Moscow's Luzhniki stadium, which will host the World Cup's opening match and final, local human rights group OVD-Info said.
Russia could run into trouble with its venue in St Petersburg, where construction has taken a decade and been marred by delays, corruption allegations and reports of human rights violations.
A new pitch had to be laid at the 68,000-seat stadium less than a month before it hosts the Confederations Cup's opening match between Russia and New Zealand, after uprooted chunks of grass spoiled the first match at the new venue.
Even before problems with the grass surfaced, issues with the stadium's retractable pitch technology saw the playing surface vibrate and made it unfit for matches.
The authorities have downplayed the lingering issues at one of Russia's most prized venues, assuring that it would be in pristine condition for the Confederations Cup. (Reporting by Gabrielle Tetrault-Farber; editing by Mark Heinrich)