For years, Democrats in Maryland eagerly soaked up campaign contributions from Baltimore Orioles owner Peter G. Angelos.

But over the past two years, Angelos has switched allegiances, becoming one of the most prolific donors to Maryland's first Republican governor in a generation, Robert L. Ehrlich Jr.

That patronage never carried quite the sting it did yesterday, when Angelos took out an advertisement in the Baltimore Sun that featured a full-page color photograph of Ehrlich, looking rugged in an Orioles team jacket, under the headline, "Thank You Governor Ehrlich."

Turns out, the ad was just the first verse in a serenade from Angelos to Ehrlich, which is meant to crescendo during a lavish tribute at Camden Yards tonight, with the governor tossing out the ceremonial first pitch.

Angelos said he bought the ad and organized tonight's event to show appreciation for Ehrlich's help when the Orioles were battling Major League Baseball over plans to move the Montreal Expos into the ballclub's back yard -- the deal that eventually brought the Nationals to Washington.

"It's my prerogative to tell the community of the sterling work that this governor did in supporting the Oriole franchise in its time of need," Angelos said in an interview yesterday. "He stepped up, we appreciate it and we're telling all the baseball fans of whatever political affiliation that Bob came forward and did, fundamentally, what any governor should do."

Democrats, though, said they're finding it very hard to distinguish these tributes from an effort to support Ehrlich's 2006 reelection campaign.

"I consider it to be an in-kind contribution," Derek Walker, spokesman for the Maryland Democratic Party, said of the ad. Moreover, Walker said, the ultimate effect of the tribute "is to associate Ehrlich with one of the most popular and enduring institutions in the city of Baltimore."

If it were counted as a campaign contribution, the ad would be a whopper. According to the Baltimore Sun's rate card, it could cost in the neighborhood of $50,000. But it will not need to be scored as an "in-kind" political contribution, said James Browning, executive director of Common Cause Maryland, since the ad lacks the "magic words" -- such as "Vote for Ehrlich" -- that would clearly identify it as a campaign promotion.

Even so, Browning said he doesn't believe that lets Angelos off the hook, at least with respect to the spirit of campaign finance laws.

"An ad like this is boosterism, which is really the same thing," Browning said.

Even without this latest support, Angelos has pushed the envelope when it comes to getting behind Ehrlich's candidacy, Browning said. In 2003, the baseball mogul gave three donations of $4,000 each to Ehrlich through separate corporate entities, skirting both the $4,000 limit on individual contributions and the $10,000 limit in total contributions to state races. Through his baseball team, Angelos also gave $10,000 to the Maryland Republican Party that year.

If this bothers Ehrlich's potential Democratic rivals, they aren't talking. Perhaps mindful of the loyalty the Orioles engender from a sizeable swath of potential Maryland voters, spokesmen for both Baltimore Mayor Martin O'Malley and Montgomery County Executive Douglas M. Duncan declined to comment.

Staff writer John Wagner contributed to this report.

Gov. Robert L. Ehrlich Jr., left, will throw the first pitch at tonight's Orioles game. Peter G. Angelos is a fan of the governor.