By Timothy Heritage

MOSCOW, May 6 (Reuter) - President Boris Yeltsin convenes Russia's Security Council on Wednesday to work out a new security concept after two fatal bomb blasts on the southern rail network.

The policy-making council, which includes top state, government and defence officials, will meet one day after a new anti-terrorist commission held its inaugural session.

``The state leadership...considers even the smallest underestimation of the importance of the fight against terrorism in the country intolerable,'' Itar-Tass news agency quoted Prime Minister Viktor Chernomyrdin as telling the commission.

He said the commission must ``as fast as possible create and work out to the finest detail a single state system of action against terrorism.''

The Security Council will seek to lay the basis for the new security system. Presidential press secretary Sergei Yastrzhembsky said the security concept was the only item on Wendesday's agenda but gave no other details.

Russia has been forced to look hard at its vulnerability to attacks, particularly in the area around Chechnya, by the bomb blasts which killed a total of four people at railway stations in Pyatigorsk and Armavir in southern Russia last month.

Yeltsin summoned Interior Minister Anatoly Kulikov for urgent talks last week after the second of the bomb blasts. A Kremlin spokesman said the president was particularly worried there could be a link with separatists in breakaway Chechnya.

Radical Chechen commander Salman Raduyev has claimed responsibility for both blasts and the Chechen authorities have opened a criminal case against him, but some Russian and Chechen officials have cast doubts on his claims.

The bomb explosions also highlighted the problems still undermining relations between Moscow and Chechnya nine months after they signed a ceasefire ending nearly 21 months of fighting over the North Caucasus region's independence drive.

Efforts have been stepped up to reach a lasting peace deal. Chechen First Deputy Prime Minister Movladi Udugov told Interfax news agency that Yeltsin would meet Chechen President Aslan Maskhadov in the first half of May in Moscow.

But sources close to the Kremlin said the meeting may take place at the end of May or in early June because of Yeltsin's busy schedule.

Many people still carry weapons in Chechnya and kidnappings are frequent. The Chechen authorities said on Tuesday they had secured the release of two Russian reporters kidnapped in March, but four other Russian journalists are still missing.

As well as reconsidering security, Russia is rethinking its defence doctrine because of the changes brought about by the collapse of communist rule and the Soviet Union in 1991.

It plans major cuts in the armed forces which Georgy Shpak, commander of airborne troops, said on Tuesday would reduce his forces by about one third to about 34,000 by September.

He told Tass he found ``many positive elements'' in the changes. But Aleksander Lebed, the former Security Council secretary who is now in opposition to Yeltsin, said in newspaper interview the decision was illogical and inexplicable.

In a sign of the problems facing the army and its low morale, Interfax news agency said a 49-year-old Russian general had leapt to his death from a window of his 15th floor apartment in Moscow. Police were treating the death as suicide.