* Hochtief, ACS shares both fall about 1.25 percent
(Adds ACS comment, dateline, updates shares)
MADRID/DUESSELDORF, Dec 27 (Reuters) - Spanish construction group ACS moved closer to control of German bid target Hochtief on Monday.
ACS said it had a total 29.27 percent of voting rights in Germany's biggest builder, up from 27.9 percent on Friday and 27.72 on Thursday thanks to shares tendered under its deliberately lowball offer of nine ACS shares for every five Hochtief shares held.
Thursday's figure excluded a 2.5 percent stake tendered by key shareholder Southeastern Asset Management, according to a source close to the deal, so ACS is already assured of reaching a key 30 percent level by a regulatory deadline on Wednesday.
Passing the 30 percent threshold gives ACS the right under German regulations to buy shares in the market to try to build its holding to its targeted 50 percent.
A spokeswoman for ACS in Germany said on Monday the company is likely to know precisely how many shares it will be able to buy by Jan. 4, 2011.
She said the company was confident it would surpass the required 30 percent but that "the (tendering) process is entirely unclear and non-transparent, who is tendering what to whom at what time".
ACS hopes to use control of Hochtief's strong balance sheet to ease the burden of its own heavy debt of more than 9 billion euros ($11.8 billion). Control of the German company would also reduce its dependence on Spain's struggling property sector and help it win bigger international deals.
The German company had fought the takeover by increasing its capital -- selling a 9.1 percent stake to Qatar. That diluted ACS's stake in Hochtief to around 27 percent from 29.9 percent, making it harder to reach 30 percent.
ACS responded by sweetening its bid, offering nine ACS shares for every five Hochtief shares, up from its previous eight-for-five offer. The offer expires Dec. 29.
Hochtief was not immediately available for comment on Monday. Shares in both companies were down about 1.25 percent on Monday morning. ACS signed a deal with the only union in Hochtief, IG BAU, last week, committing to maintain working conditions until 2013 once its full acquisition of the company is completed.
(Reporting by Paul Day in Madrid and Anneli Palmen in Duesseldorf; Writing by Nicola Leske; Editing by Mike Nesbit) ($1=.7625 euros)