Shifting demographics and changing spending habits in Prince George's County have contributed in recent years to the decline of small and often-rundown neighborhood shopping centers, according to recent reports prepared by the Maryland-National Capital Park and Planning Commission.

Planners told the County Council yesterday that the retail trade industry in Prince George's accounted for 50,000 jobs, $663 million in wages and $3.7 billion in sales between 1972 and 1982.

During that period, according to the commission, county consumers' spending was up in restaurants but down in drugstores and general merchandise-type outlets that are often the mainstay of small shopping centers.

That change in purchasing habits reflected an increase in one- and two-person households and a larger number of married women in the work place, planners said.

Although the number of retail outlets in the county has increased, some council members complained that the county government has not placed enough emphasis on revitalizing older areas and bringing in different types of retail development.

"As long as we don't have a Saks and a Bloomingdale's, we go to Virginia and Montgomery County to shop," council member Floyd E. Wilson said.

"You find the Pace stores, the Makro stores coming," he added, referring to two membership warehouse stores that are expanding in the county. "You don't see them anywhere else."

Of the county's 62 neighborhood shopping centers, 10 were identified by planners as being in economic distress because of high vacancy rates. Council member Sue V. Mills said that one of the reasons these centers are in decline is that developers are more anxious to build on the 16 million square feet of vacant industrially zoned land than to renovate occupied sites.

Council administrator Samuel Wynkoop warned the council that piecemeal rezoning of individual tracts of land to accommodate such new development contributes to the problem.

Earlier this week, the council delayed action on just such a case in Glenn Dale, where residents have complained that a planned shopping center would change the character of a residential neighborhood and would run counter to land use plans adopted as county policy.

Warren Rosenthal of the Prince George's County Economic Development Corp. said his organization has received inquiries from developers interested in purchasing and renovating several older shopping centers.

"The market is changing, the demographics are changing," Rosenthal said. "So that requires a change in the look of the stores . . . and a change in the mix of tenants."

"The corporation is not ignoring the strip centers," he said. "We are very concerned about those, and that will be the next step for us."

In other business yesterday, legislation was introduced that would require lawn pesticide companies to post notices on public and private property before and after a chemical application is made. The bill, sponsored by council member Frank Casula, is similar to an ordinance pending in Montgomery County.

Casula, citing potential health problems from applications of such substances, persuaded the council to include an amendment to the bill that would exempt people who spray their own lawns from the provisions of the measure.

The council spent several hours yesterday amending legislation that will create a quasi-public Prince George's County Parking Authority with the power to float $12 million in revenue bonds to build a parking facility for the proposed Hyattsville Justice Center.