UPDATE 2-US offshore tax bill in coming weeks-aide

* U.S. Senate Finance Chairman to introduce bill

* Bill seen as less punitive than rival effort

* U.S. says loses $100 bln a year from tax evasion (Adds detail on timing, UBS lawsuit filings due Thursday in paragraphs 1, 8-10)

By Kim Dixon

WASHINGTON, April 29 (Reuters) - The chairman of the U.S. Senate Finance Committee plans to introduce legislation in the coming weeks to give U.S. tax collectors more tools to police offshore tax evasion, an aide to the senator said on Wednesday.

The draft bill, sponsored by Democratic Senator Max Baucus, seeks to deter offshore tax havens by increasing reporting requirements to the Internal Revenue Service for entities transferring funds offshore and puts more onus on tax preparers to root out wrongdoing.

Evasion of taxes using foreign accounts by individuals and corporations is said to cost the U.S. government $100 billion a year, according to a congressional report.

But the Baucus effort is narrower in scope and seen by some as more lenient than an earlier proposal introduced by Democrat Senator Carl Levin, chairman of an investigative committee in the Senate that has studied and issued influential reports on the topic.

President Barack Obama supported Levin's effort to cracking down on tax havens before he left the Senate for the White House.