Window dressing, position squaring, marking up. Call it what you will, portfolio managers' last-minute maneuvers are having a pronounced effect on the market in the waning days of the quarter.

Although no mutual fund or hedge fund manager will ever admit to it, a lot of tidying up goes on at the end of a quarter. First, there's the buying and selling that occurs to make a portfolio look better -- having a big loser on the list of top holdings sent out to investors will not do. Better to own

Boeing

(BA) - Get Report

, the aircraft maker whose recent chart looks like tech stock charts used to.

Then there's marking up stocks -- driving a core holding higher to eke out a higher return on the quarter. You own a lot of

General Electric

(GE) - Get Report

, you give it a goose. It's a dangerous game -- the demand that's created for a stock is essentially artificial, and a portfolio that gains ground from marking up this quarter will give it back in the next -- but if you're fighting to keep your head above water, you'll do it.

"With the quarter teetering on being down, I have no doubt that people are going to do their damndest to get stocks up," says Seth Tobias, manager at the New York-based hedge fund

Circle T Partners

. "I see major buyers in certain mega-cap stocks."

A lot of people are fighting to keep their heads above water this quarter. On June 30, the

Wilshire 5000 Total Market Index

-- the index that most closely matches the performance of the entire U.S. stock market -- closed at 13,618. Thursday it was trading at 13,698, putting it about even on the quarter. Even though they're all geniuses, average fund managers tend to bring in returns that match those of the overall market pretty well. Some will do much better, some will do much worse, but most will muddle through. Muddling through means breaking even, which is bad. Your investors notice it. And they probably have an in-law who did better.

So you do something to keep it from happening.

Ordinarily, that might set things up for a nice run at the end of the quarter, but some are crosscurrents. "A couple of accounts are telling me they are hearing institutions are getting rid of losers," wrote one trader in an instant message Wednesday. "Since so many stocks, e.g., telecom, have been crushed, it doesn't do any good to mark them up."

Here it gets hard. Are institutions selling telecom equipment because they want nicer-looking portfolios, or are they selling them because of genuine fears about telecom capital spending? There's a reason the stocks haven't done well this quarter, and with earnings season around the corner, there's a bit of panic in the air. Ditto Internets. Did they get sold off Wednesday because

priceline.com's

(PCLN)

warning blew the quarterly performance for all dot-coms, or were investors worried that priceline's trouble augured poorly for

Yahoo!

(YHOO)

?

"I'm not sure we would see any different action if it wasn't quarter-end," says Pete Boockvar, equity strategist at

Miller Tabak

. "People have no tolerance for disappointments and people are running scared. Look at

Motorola

(MOT)

," which took a dive Wednesday morning on

rumors of an earnings miss. "Just on the whiff of a rumor they puked the stock down."