If you buy toothpaste, laundry detergent or disposable diapers -- and that takes in just about everybody -- you probably know why the folks at Procter & Gamble Co. are so glum these days.

The company's Crest toothpaste, Tide detergent and Pampers diapers are being crowded for space on the nation's store shelves by all sorts of new competitors -- many of them offering superior quality and chipping away at the company's huge market share in these product lines.

The increased competition in these markets and the many others in which P&G competes is taking its toll on the consumer-products giant. The costs of fighting these battles and of rolling out a host of new products are mounting, so much so that Procter & Gamble on Thursday is expected to announce its first decline in annual profits in 33 years.

Wall Street analysts, who began predicting the earnings decline a few months ago, say Procter & Gamble is by no means on the ropes -- it is still a phenomenally successful and profitable enterprise. But they say the company is in for a long fight to check the declines in market share and profits and to regain some semblance of its once-dominant position.

"The lead will never be as wide as it once was. The world has changed too much," says Jay Freedman, an analyst at Kidder Peabody. "The competitive activity in their basic business has gotten a lot stronger, and they've had some pretty aggressive growth plans that have been a little bit slower in coming around than they had anticipated."

Executives at Procter & Gamble's Cincinnati headquarters, traditionally taciturn in the best of times, have been even more so on the subject of the company's fiscal 1985 results. But P&G has been preaching reduced expectations to its shareholders in its past couple of annual reports and shareholders meetings, and a company spokesman said last week of the predictions of an earnings decline: "That's everybody's guess, and it's a good one."

By Wall Street reckoning, Procter & Gamble will report earnings for the year ended June 30 of about $640 million -- equivalent to $3.85 a share -- on sales somewhere in the neighborhood of $14 billion. Last year, the company earned $890 million ($5.35 a share) on $12.9 billion in sales.

The last time Procter & Gamble had a year with earnings like those anticipated was 1980. But those were the good old days, when it seemed like P&G could do no wrong. Products like Ivory soap, Folger's coffee and Duncan Hines cake mixes -- in addition to Pampers, Crest and Tide -- were seemingly staples of every household in America. Procter & Gamble had a reputation as the nonpareil marketer of consumer goods and the producer of extremely skilled sales and marketing experts, contributing its alumni to the marketing divisions of many other American corporations.

But other companies began figuring out P&G's formula for success -- technological advances, careful market research and aggressive selling -- and began competing with the giant on its own terms in several key P&G product areas. The tough new competition, in addition to some blunders by P&G, began eating into the company's share of some markets it once ruled.

"They've been losing market share in many of their consumer products since the 1970s," says Jack Salzman, an analyst who follows the company for Goldman Sachs.

Pampers disposable diapers, for instance, which analysts estimate account for $1 billion in P&G's annual sales and no less than 20 percent of the company's earnings, have lost several percentage points of market share in recent years as Kimberly-Clark's Huggies and other competitors have come up with better diapers and consumers have shown a willingness -- much to P&G's surprise -- to pay more to get them.

"Basically, Pampers was an inferior diaper, it was a middle-of-the-road diaper," neither budget nor top quality, "and middle products don't do very well," says Hugh Zurkuhlen, an analyst at Salomon Brothers. P&G struck back earlier this year with the much-heralded introduction of a more absorbent version of Pampers, but analysts say that at best that move may only check the decline in market share.

The company has had similar problems in toothpaste, where other companies have come up with better-tasting formulas, gels and pump dispensers -- all of which P&G's Crest was slow to emulate. The result, again, was a market-share slump.

Trying to get even with its upstart competitors, P&G has unleashed a raft of new and improved products in the past couple of years, with mixed results that seemed to indicate that P&G's marketing prowess, once seemingly invincible, had eroded.

"They've been rolling a lot of products out," Freedman says. "They've had less than super success."

Such new offerings as Duncan Hines cookies and Citrus Hill orange juice have been slow to gain market acceptance, in part because they are running up against particularly stiff competition -- the cookies, for instance, must compete against Keebler, Nabisco Brands, and PepsiCo's Grandma's subsidiary.

"Everybody and their grandma -- including Grandma's -- came out with a cookie against them," Salzman says.

Such tough competition has become common for P&G. In part, it is due to the fact that most consumer-products companies, coming off of flush years in the early 1980s, poured money into developing and introducing new products -- many of which were targeted right at P&G.

"It's no accident that so many new products came against them at one time," Salzman says, adding, "The guys who cranked up new product cycles against P&G cranked up better ones."

In addition, P&G became something of a victim of its own considerable success. As the company has grown, it has struggled harder and harder to find big winners to sustain that growth.

It generally takes a series of major technological breakthroughs to keep up such massive growth, and P&G hasn't had many of those since the successes of fluoride toothpaste and the original concept of Pampers a couple of decades ago. Some of the company's breakthroughs in the interim have been less than rewarding, such as Pringle's potato chips and Rely tampons, which fell victim to the toxic-shock scare in 1981.

P&G's best hope for the future currently is a material called sucrose polyester, a revolutionary synthetic fat that can reduce cholesterol levels in food. But sucrose polyester is still years away from the marketplace.

Lacking technological hits, and in search of products with maximum potential, P&G has had to enter some fairly large and hotly contested markets, such as cookies and orange juice.

"It's very difficult to grow a company that's $14 billion in sales," Zurkuhlen says. "For that reason, to have anything meaningful you have to go into big markets, and in big markets, there's big competition."

Duncan Hines cookies have only captured about 5 percent of the huge but crowded cookie market, and in orange juice, P&G "spent $150 million in the past 18 months for a whopping 8 percent of the market," Salzman says sardonically.

That cost and other expenses of developing and advertising a whole flock of new products have also cut into P&G's earnings, with analysts estimating the company's overall new-product expenditures at $500 million over the past few years, including $150 million in the fiscal year just ended.

"That's a big expenditure that wasn't originally anticipated in the earnings estimates," Salzman says.

Since most of P&G's product-introduction costs are now behind it, analysts expect the company to show a bit of a rebound in its new fiscal year.

"The overall trend in their market shares seems to be firming, and in some cases is beginning to come back up," Salzman says.

At the same time, P&G's competitors are slowing down a bit. "Those factors should allow Procter's earnings to recover," Salzman says. "The question is not so much are they going to recover, but how much are they going to recover."

Still, the company that once towered over the consumer-products industry has been humbled a bit, and it may never regain all of its former dominance in the more competitive environment of today. "The Procter & Gamble that people had an image of just doesn't exist today," Salzman says.

And Freedman says, "The ability for them to be consistently dominant is in the past."