A new round of spending by Penn National Gaming and MGM Resorts International has pushed the ad war in the referendum over expanded gambling into record territory -- eclipsing the $34 million raised for the 2006 governor's race with four weeks to go before Election Day.

In a filing posted Tuesday with the State Board of Elections, the ballot committee financed by Penn National reported that its outlay for the effort to defeat Question 7 has reached $21.6 million -- $18 million of which has been spent. The pro-expansion committee reported that it has spent $17.7 million, $14.4 million of it supplied by MGM and the rest by its allies at Caesars Entertainment and the Peterson Cos.

The combined spending of $35.7 million exceeds the amount spent by Democrat Martin O'Malley and Republican Robert L. Ehrlich when O'Malley ousted the incumbent governor.

MGM is the prospective developer of a casino at Peterson's National Harbor in Prince George's County -- one of the sites permitted if voters approve the gambling expansion plan adopted by the General Assembly. Penn National is fighting the plan, contending that it puts its Rosecroft Raceway at a disadvantage in the competition for a casino license. Penn National is also concerned that a National Harbor casino could cut into business at its Hollywood Casino in Charles Town, W. Va.

Caesars, an affiliate of which holds the license for a planned casino in downtown Baltimore, supports the referendum because its would clear the way for it  and other casinos to offer table games.

With all the potential gambling revenue at stake, Maryland television viewers can look forward to several more weeks of watching competing casino companies hammer each other with sacks of cash. This may be why the mute button was invented.