A trio of deals were abandoned yesterday by companies facing tough scrutiny by the Federal Trade Commission, the latest sign that antitrust regulators are casting an increasingly skeptical eye on mergers and acquisitions.

Viacom's Blockbuster Inc. video chain backed off its proposed franchise agreement with Hollywood Entertainment Corp., one of its largest rivals, after the FTC expressed objections to the arrangement.

Meanwhile, Royal Ahold NV, the Dutch supermarket conglomerate, announced that it will walk away from its $1.75 billion purchase of Pathmark Stores Inc.'s New Jersey stores after encountering what company officials called "strong opposition" from the FTC.

And finally, pharmaceutical giant Abbott Laboratories Inc. canceled its plans to buy drugmaker Alza Corp. for $7.3 billion.

The timing of the decisions was purely coincidental, but it suggested that Clinton administration enforcers are more wary than ever about the pace and scale of consolidation in a variety of industries. The agency doesn't have the power to block acquisitions outright, but it can insist on conditions that are so stringent that the deal is no longer palatable to the merging parties, and it can threaten to tangle up matters in litigation for years.

As the merger wave continues, specialists say, both the FTC and Justice have raised the hurdles for companies seeking to merge and ally with rivals, concerned that further consolidation will harm consumers by leaving market power in the hands of a shrinking pool of competitors.

But it's not merely that the FTC is getting harder to please, according to experts. Swept up in the merger craze, many companies today are proposing deals that would have been unthinkable only a decade ago.

"Companies are getting bolder," said George Hay, a professor at Cornell University. "It shouldn't be a surprise that the agency is knocking some of these deals down."

The FTC's head of enforcement, Richard Parker, explained that the agency's activism stems from its sense that in the past, it was occasionally too willing to approve certain deals once the parties agreed to divestitures. In some instances, when companies sold off product lines to satisfy the FTC, the company that purchased the assets lacked the wherewithal to truly compete.

"This is all 20-20 hindsight," Parker said. "But when you demand that a company divest certain assets, you often carve it up so badly that you take apart a functioning business, and who knows whether the company you divested can pick up the ball and compete."

Abbott executives said they had spent five months trying to win over FTC enforcers and had agreed to sell off one of Alza's product lines--an experimental prostate cancer treatment--but failed to convince FTC staffers that the deal was good for competition.

Officials at Royal Ahold, which bought Giant Food Inc. last year, released a statement yesterday decrying the FTC's opposition.

"We believe that the regulators' position represents a distinct departure from past policies," the statement said. "We have made every effort to get the transaction approved."

Many of Pathmark's 135 stores are in New Jersey, where Ahold already has a fairly strong presence, according to the FTC. The extent of the overlap led the agency to conclude that even if Ahold sold off certain stores, the company would be powerful enough to raise prices and its new competitor would not be as vigorous a competitor as Pathmark.

"The footprints of those companies are quite close," Parker said.