The Russian intelligence agency has been stepping up its activity in Israel, say security officials, who have been worried by signs that Russia has been collecting information on Israel.

Security officials believe that agents, who have kept up connections with the Russian intelligence agency, have infiltrated into the country along with the hundreds of thousands of immigrants that came to Israel from the former Soviet Union during the past decade.

Senior officials have also expressed concern over the malfunctions of the Nativ organization, the liaison bureau providing aid for Jews in the former Soviet Union and its emigrants in the United States and Europe. According to officials, the organization does not systematically confirm the identity of many of the emigrants who have received Israeli citizenship with the help of Nativ, and it is likely that people affiliated with organized crime, as well as Russian intelligence agents, have been able to enter the country with the help of this organization.

The police unit for international crime investigation received unconfirmed information last week of the existence of a 1997 recording of conversations between then infrastructure minister Ariel Sharon and the Russian energy corporation Gazprom chair Ram Viakirev.

The content of these conversations was the basis for a police investigation carried out in 1999, which looked into questionable connections between Sharon, Major General (Res.) Avigdor Ben-Gal and Gazprom chiefs. If such a recording exists, say sources, it could provide evidence for reopening the case and pressing charges against Prime Minister Sharon, or could be used to blackmail the prime minister.

Sharon was suspected in 1999 with helping Ben-Gal advance his business interests, in return for Ben-Gal's changing his testimony in Sharon's libel suit against Ha'aretz.

Investigators suspected that Sharon had asked Viakirev for preferential treatment for Ben-Gal, who was chair of Israel Aircrafts Industries at the time, when he took Ben-Gal with him on a diplomatic visit to Russia in June 1997. After the trip, Ben-Gal, who had originally been on the list of Ha'aretz's witnesses in the lawsuit, testified on Sharon's behalf about events in the 1982 Lebanon War.

Although Attorney General Elyakim Rubinstein and State Prosecutor Edna Arbel decided to close the case without pressing charges because police said they had not found enough evidence on which to base a lawsuit, they reprimanded Sharon for his alleged behavior.

According to new information received by police, senior Russian sources told their Israeli business partners they had heard that the conversations between Sharon and Viakirev had been recorded and could pose a problem for Sharon if publicized.

The sources admitted they had not heard the recordings themselves and are only passing on rumors, but believe that such a recording could be used by Russian intelligence agencies or Russian organized crime to blackmail the prime minister.

Head of the police unit, Brigadier General Moshe Levine, nevertheless decided not to reopen the case unless the actual recording is obtained.