(Adds deal detail from paragraph 2, analyst quote in paragraph 5, S&P/ASX200 index opening in paragraph 6)

April 26 (Reuters) - BHP Group shares fell 4% on Friday in the first day of trading of its Australian-listed stock since revealing a $38.8 billion bid for smaller rival Anglo American in a deal that would forge the world's largest copper miner.

BHP said it would offer 25.08 pounds ($31.39) per Anglo share, a premium of 31% from the stock's previous close before the bid was made public on Thursday.

Anglo shares rose 16.1% to 25.60 pounds in London trading on Thursday.

BHP's shares fell as much 4.5% in early trading on Friday. The stock did not trade on Thursday as the Australian share market was closed for a holiday, meaning Friday's trading is the first reaction from investors to the mega takeover plan.

"With concerns over China growth and softening commodities forecasts, the market is drawing the conclusion that this is a top of cycle deal and BHP is overpaying," said John Milroy, private wealth advisor at brokerage Ord Minnett, refering the share price fall.

The benchmark S&P/ASX200 index was down 1.3% in early trade.

BHP has until May 22 to make a binding bid. There is already early opposition from Anglo management which does not consider the offer as attractive enough, Reuters reported citing sources.

A deal, if successful, would be the largest mining takeover globally in 2024 and in the top ten largest deals for the sector ever, according to LSEG data.

Under its plan, BHP plans to spin out Anglo's iron ore and platinum assets in South Africa, where BHP, the world's largest listed miner, has no activities. (Reporting by Scott Murdoch in Sydney and Melanie Burton in Melbourne; additional reporting Archisma Iyer in Bengalaru. Editing by Christian Schmollinger and Sonali Paul)