On Wall Street, they're calling it one of the worst cases of "bad breadth" in modern memory.

A few big-name stocks have been strong through the early summer, carrying some of the market indexes to new highs. But thousands of other stocks, particularly those of smaller companies, are languishing.What analysts call market breadth - the number of advancing stocks versus the number declining - struggles along way behind the averages' progress. That explains why big bull-market gains aren't showing up in the portfolios of many individual investors or mutual funds, except those funds that specialize in large growth companies.

Sign of the times: Standard & Poor's Corp. reports that just 15 elite stocks - names like Microsoft, Intel, General Electric and Coca-Cola - now make up 25 percent of the total market value of S&P's 500-stock composite index.

Thanks to stalwarts like these, the S&P composite index boasts a return of better than 15 percent for the year to date, while broad indexes of smaller stocks barely show a gain at all or even have slipped into negative territory.

"Probably the most frustrating aspect of the present market environment is its narrowness," says Byron Wien, investment strategist at Morgan Stanley Dean Witter & Co.

By some measures, the trend in favor of consistently growing blue chips, and away from smaller companies and undiscovered value stocks, has been in force for three to four years now.

It has gone on so long it has turned into a movement of its own, complete with a name - "momentum investing" - and a growing body of commentary to explain why it has occurred and how it may continue indefinitely into the future.

Investors who follow the trends in the market from day to day or week to week are left with a dreadful sense that anyone who sticks with small stocks, or value stocks, instead of blue-chip growth, is committing some grave error in judgment.

Analysts suggest that big stocks will keep excelling because of demand from multi-billion-dollar mutual funds. These funds are so big that only big stocks will work in their portfolios, the reasoning goes. Besides, they want to own the big stocks because those are the ones that are doing well.

But many diehard fans of small and mid-size companies say this circular effect won't keep repeating forever. The longer it continues, they say, the more overpriced big stocks get, and the more attractive small stocks become by comparison.

Ultimately, these observers say, stock prices must be determined by the earning power of the companies they represent. So big stocks can't keep running ahead of the rest of the pack unless earnings of big companies do likewise.

"The Dow blue chips and the S&P big caps are likely to remain high-priced relative to growth, because they are still attracting lots of mutual and pension fund money that is seeking presumed safety and quality," says Stephen Quickel in his newsletter U.S. Investment Report.

"But their growth potential is limited. Meantime technology and other growth stocks, including a smattering of medium- and small-caps, have greater appreciation potential because of their underlying earnings drive."

In the eyes of Richard Moroney, editor of the advisory letter Dow Theory Forecasts in Hammond, Ind., "Plenty of good values remain in the small-cap sector, but most have been ignored in the market's latest flight to quality.

"Playing the small-cap segment of the market may require continued patience. But investors looking for longer-term gains shouldn't overlook the growth potential many small-cap companies offer."