MANILA (Reuters) -- Plans to debate changing the constitution and alter the political system by allies of Philippine President Gloria Macapagal Arroyo have been shelved after opposition from powerful religious groups.

"We are not insensitive to public opinion," Jose de Venecia, Speaker of the House of Representatives, told reporters late on Monday.

De Venecia triggered a storm last week when the House voted to exclude the Senate from voting on shifting from a presidential system to a unicameral parliamentary setup, which would abolish the upper house, stacked with Arroyo's foes.

Powerful Catholic bishops had called for nationwide prayer rallies on Sunday to demonstrate against the lower house's move, which they branded, "scandalously immoral".

Leftist groups said they would stage rallies this week and security sources said concerns about possible political unrest in Manila had influenced Arroyo's decision to postpone a Dec. 11-13 summit of Asian leaders in the central Philippines till January.

To cool the political temperature, De Venecia said the lower house would now call for elections next year -- coinciding with congressional and local elections -- for delegates to a constitutional convention, which would look at altering the charter.

A constitutional convention, composed of legal luminaries and representatives from civil society as well as politicians, would be more palatable to opposition groups and the wider public.

"A constitutional convention is a bit of an appeasement strategy," said Erin Prelypchan of Manila-based Pacific Strategies & Assessments. "But how they are going to decide who gets a vote in a constitutional convention, that could attract a lot of potential opposition."

The influential Catholic Bishops Conference of the Philippines (CBCP) said it would push on with a prayer rally on Dec. 17 in Manila, where thousands are expected to attend, but it asked followers to avoid bringing political banners and placards. "What they (the lower house) did Monday night did not solve our problem," Monsignor Pedro Quitorio, CBCP spokesman, told local radio. "What we still need is prayer."

The Philippines is a mainly Catholic country and the church is a key political player but analysts do not expect Sunday's gatherings to spark a campaign to oust Arroyo, who has survived two impeachment bids and one coup attempt.

The country's small middle class -- instrumental in the overthrow of two presidents -- is fed up with political turbulence and with an improving economy shows little stomach for ousting the current administration, as unpopular as it is.

Arroyo has championed altering the political system to end gridlock between the legislative and executive branches of government and between the two houses of Congress.

But critics accuse Arroyo, due to step down in 2010, of trying to use the proposed change to extend her term in office.

Under the plan, the president and a newly created prime minister would share power for three years. After 2010, the prime minister would become head of a British-style Parliament.