* AbbVie slides after $63 bln deal to buy Allergan
* Lennar rises after qtrly profit beat
* Fed Chair Jerome Powell to speak at 1:00 p.m. ET
* Futures down: Dow 0.06%, S&P 0.12%, Nasdaq 0.15% (Changes comment, adds details; updates prices)
By Medha Singh
June 25 (Reuters) - Wall Street's main indexes were set to open slightly lower on Tuesday, as investors worried about the fallout of new sanctions on Iran and signs that talks with China may generate little progress on trade.
After three weeks of steady gains on the prospect of more monetary stimulus for the economy and markets, all eyes will be on speeches by Federal Reserve policymakers that are widely expected to point to a cut in interest rates next month.
A senior U.S. official said President Donald Trump is "comfortable with any outcome" from the talks with his Chinese counterpart, dampening any hopes that the United States and China would be able to strike a trade deal at the G20 summit later this week.
"It is unlikely that any resolution of the trade situation will take place until after the next Fed meeting late next month," said Robert Johnson, chief executive officer at Economic Index Associates in New York.
A trade resolution will allow the Fed to forestall any interest rate cut, Johnson said. "I believe what Trump wants is both a Fed rate cut and to declare victory in the trade dispute with China."
Wall Street's main indexes have risen at least 7% this month, with the S&P 500 hitting a record high last week.
Traders fully expect a rate cut from the U.S. central bank in July and see a 40% possibility of a 50 basis point move, CME Group's FedWatch program showed.
In a dramatic and unprecedented move, Trump on Monday imposed new sanctions on Iran's supreme leader and foreign minister, a decision Tehran said closed the path to diplomacy between the countries.
At 8:30 a.m. ET, Dow e-minis were down 17 points, or 0.06%. S&P 500 e-minis were down 3.5 points, or 0.12% and Nasdaq 100 e-minis were down 12 points, or 0.15%.
Among stocks, AbbVie Inc slipped 8% after the drugmaker said it would buy Botox-maker Allergan Plc in a cash-and-stock deal for about $63 billion. Shares of Allergan surged 31.9%.
Lennar Corp rose 3.6% after the No. 2 U.S. homebuilder reported a higher-than-expected quarterly profit.
On the economic front, the Commerce Department is expected to announce that new home sales rose to 680,000 units in May from 673,000 a month earlier.
Separately, the Conference Board is expected to report consumer confidence fell to a reading of 131.2 in June from 134.1 in May. Both sets of data are due at 10:00 a.m. ET. (Reporting by Medha Singh and Aparajita Saxena in Bengaluru; Editing by Anil D'Silva)