NEW YORK – Are the best days of the buyout boom that has shored up the stock market’s recent rally almost over?

Market experts differ on the likelihood of that happening.

Merger activity has been very robust this year, observed one news source, with the value of deals announced through Wednesday jumping to $544 billion in the U.S. That’s up from $411 billion at the same time in 2006.

Last year, by the way, turned out to be a record year for mergers and acquisitions.

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Deals announced this month alone include the proposed $25 billion buyout of college loan provider SLM — better known as Sallie Mae — as well as the $29 billion takeover of credit card and payment processor First Data Corp.

While market analysts cited various factors that helped push the rebound in stocks to two record highs on Wednesday and Thursday, a focal point for the market has been deal activity. Big deals are encouraging to investors, analysts say, because they can be a sign that other companies may get bought, typically at a premium to their stock prices.

Fueling the latest round of mergers and buyout have been private equity firms that buy companies with mostly borrowed funds and try to grow or turn around the target and eventually sell out for a profit, usually within three to five years.

In the first quarter of this year alone, private equity firms accounted for nearly 26 percent of overall U.S. deal activity, and three of the top 10 deals announced involved private equity buyers, Thomson Financial reported.

Analysts concur that investor enthusiasm for private equity funds shows little sign of abating. In fact, one private equity research firm expects private equity funds to raise $550 billion this year. That would top the record $432 billion raised in 2006.

Still, some market experts have opined that industry plays are beginning to worry about market conditions.

Competition has gotten intense for deals, said one news source, that prices paid for companies are rising. In addition, eager lenders are financing many deals that shouldn’t even get done in the first place, they said, a sign that the market may be headed for a downturn.

One private equity expert offered that some portfolios may have loaded up too much on debt. A tightening of credit, which has fueled the buyout boom, would rein the market in.

Still others have speculated that a pullback in buyout activity won’t slow down and that private equity has become more mainstream.

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