FRANKFURT, April 30 (Reuters) - Business software maker SAP (SAPG.DE: Quote, Profile, Research) posted disappointing first-quarter results as a weak U.S. economy started to bite, and delayed targets for new software on which its growth plans depend, hitting its shares.

SAP reached the lower end of its full-year target range for growth in software and software-related services sales and kept its sales forecast on Wednesday as it begins to integrate Business Objects, its biggest-ever acquisition.

But the 15 percent rise in software and software-related service sales, SAP's key metric, was less than the market had expected. At constant currencies, SAP said the increase would have been 24 percent.

SAP said the U.S. market had been hard, echoing last month's comments from rival Oracle (ORCL.O: Quote, Profile, Research).

"The U.S. market in the first quarter was tougher than expected," Chief Executive Henning Kagermann told a conference call for journalists. "We continue to watch the U.S. market closely."

SAP's results continued a dismal trend in this quarter's software earnings, a change from recent quarters when vendors of corporate software had appeared shielded from the effects of a U.S. economic slowdown.

Oracle posted weaker-than-expected software sales last month and some smaller software makers such as Software AG (SOWG.DE: Quote, Profile, Research), Lawson (LWSN.O: Quote, Profile, Research) and Epicor (EPIC.O: Quote, Profile, Research) also disappointed.

"SOFTER THAN EXPECTED"

Shares in SAP -- whose software helps large firms to automate, integrate and manage their businesses -- fell more than 6 percent and by 0935 GMT were down 4.4 percent at 31.59 euros, the biggest losers in a flat DJ Stoxx 50 .

The stock is down 7 percent since the start of the year, underperforming Europe's technology index by 11 percent, but at 18 times 2008 earnings, according to Reuters Estimates, analysts say it is still expensive compared with the sector.

"Amid little-inspiring results and in-line guidance, plus a fairly weak Business Objects contribution, we believe the risk factors still outweigh the opportunities," Cheuvreux analyst Bernd Laux wrote in a research note.

UniCredit analyst Knut Woller wrote: "Based on the softer-than-expected start into the year... we see the risk that the full year growth targets could be missed."

SAP raised its non-GAAP operating margin target for the year by one percentage point to 28.5 to 29 percent at constant currencies, compared with last year's 27.3 percent, as it halved planned investment in its new Business ByDesign software.

It said it would now take 12 to 18 months longer than the originally planned date of 2010 to reach 10,000 customers and $1 billion in revenues with the product, SAP's first foray into the world of hosted software pioneered by Salesforce.com (CRM.N: Quote, Profile, Research).

Kagermann said he was not worried that SAP would lose market share to rivals in the meantime because SAP's on-demand software would have more functions than that of Salesforce.com or Netsuite (N.N: Quote, Profile, Research), who concentrate on customer relationship management.

Kagermann has said raising SAP's margins above 35 percent in the long term depends on the successful development of Business ByDesign as a volume business.