NEW DELHI (Reuters) - Indias federal investigator is probing 21 sizeable companies for links to a bribes-for-loans scandal that has hit lending and infrastructure shares and rocked the countrys image as an investment destination. Eight financial executives from the public and private sectors have been arrested in the scandal, one of several to dog the government of Prime Minister Manmohan Singh and test Indias ability to crack down on corruption. Many of the companies the federal Central Bureau of Investigation (CBI) has linked to the case are connected to the booming infrastructure sector-builders of dams, power plants, energy equipment makers and property developers. Shares in these sectors fell sharply on Friday. The CBI is also looking into the involvement of fund managers and senior officials at state-run insurance companies in all deals arranged by Money Matters Financial Services, the firm cited as the mediator on the deals. The CBI is also probing all block deals, bulk deals and share placements arranged by Money Matters, a source with direct knowledge of the matter told Reuters. Bond and rupee markets in one of the worlds fastest growing emerging economies remained unaffected as traders did not view it as a risk to the banking system. Analysts said the scandal, coming just a few days after Singh defended his government in another case involving mobile phone licences sold for below-market prices, could harm investor sentiment. If we can clearly say that we have done something right at this point in time and do proper things at this point in time then its salvageable but otherwise it does have a potential to impact investor sentiments towards India from a medium-term perspective, Nitin Jain, Singapore-based principal of fund manager Kotak Mahindra. Ratan Tata, one of Indias most powerful businessmen, criticised the Indian government in a rare interview. I wish the government would take a stand, bring order...have an investigation, book people who are guilty of something, he said in an excerpt from an interview to be aired on Indian broadcaster NDTV on Saturday. Investors so far remain keen to tap into a country with a young and fast-urbanising population of 1.2 billion. Economic growth is forecast at 8.5 percent in 2010-11, and between 9 and 10 percent a year after that, rivalled only by China among major economies. But repeated scandals in recent months have marked a change from the days when corruption and graft command little space or time on the countrys top media outlets. Analysts say this is due to the explosion of 24-hour television channels, a more assertive opposition and a growing middle class fed up with rampant graft throughout society. Notices have been sent to 21 companies. It includes big to medium size companies, including real estate companies, a CBI official, who did not want to be named, told Reuters. Preliminary evidence points to the fact that the case is limited to individuals. So fall-out is unlikely to be big. Several leading Indian companies have acknowledged that they have been asked for information. Some were already named in court documents filed by the CBI on Wednesday and include the worlds third largest wind turbine maker Suzlon Energy. Suzlon has denied any wrongdoing. On Wednesday, federal agents arrested senior officials at state-run Central Bank of India, Punjab National Bank and Bank of India-all major banks with operations across the country. The CBI said the executives had received bribes from Money Matters. Three senior Money Matters executives were also arrested on charges of handing out bribes. Shares in real estate and energy sectors have fallen over the past few days on fears that a cash crunch could delay or derail major development projects, some key to Indias ambitious infrastructure expansion goals. India was ranked 87th in Transparency Internationals 2010 ranking of nations based on the perceived level of corruption. India lies behind rival China, which is in 78th place.