Margaret Beckett repeatedly rejected calls by MPs on all sides to condemn Israel's actions in the Lebanon.
Mrs Beckett said Hezbollah had no justification for attacking Israel
The foreign secretary said she had condemned Hezbollah but bowing to MPs' demands on criticising Israel was not the most effective policy.
Shadow foreign secretary William Hague said he thought "elements of Israel's response are disproportionate".
It came as the UK pledged £2m towards relief efforts in the Lebanon after an appeal by the Lebanese prime minister.
Mr Hague told MPs the right of Israel to defend itself was "clear" and calls for an unconditional Israeli ceasefire were "futile" unless rocket attacks on it stopped and captured soldiers returned.
But the Tory frontbencher said Israel's "disproportionate" response was delaying efforts to bring about a ceasefire.
"I think we can say that elements of the Israeli response are disproportionate, including attacks on Lebanese army units, the loss of civilian life and essential infrastructure and such enormous damage to the capacity of the Lebanese government, [which] does damage the Israeli cause in the long term," he told MPs.
That was still the case even if military units in the Lebanon were "callously" stationed in civilian areas.
Labour MP Louise Ellman said it was proportionate for Israel to defend itself against unwarranted aggression.
But Labour former Cabinet minister Clare Short accused ministers of "inflaming" the situation by pursuing an "unbalanced and morally wrong" policy.
Ms Short told the Commons "massive killing of innocent Lebanese civilians and destruction of infrastructure" was so disproportionate that it amounted to a war crime.
More Lebanese people were being killed than Israelis, argued Ms Short, but "the way we talk it sounds as though we are saying an Arab life is not as important as an Israeli life and that is profoundly wrong".
She warned: "We are, I'm afraid, heading for further violence and catastrophe and I'm sad to say that our government is following President Bush's errors and pouring petrol on the flames."
Liberal Democrat spokesman Michael Moore said an urgent ceasefire was needed to stop the crisis spiralling around the world.
Even the perception that the US was willing to give the green light to Israeli military action for a few more days was deeply damaging, added Mr Moore.
The debate came as the evacuation of UK citizens from Lebanon was stepped up.
Mrs Beckett said the government had urged all parties to act "proportionately and that they should do everything possible to avoid civilian violence".
And she stressed that she regretted deaths on all sides.
Ex-Labour Foreign Office Minister Chris Mullin asked Mrs Beckett if it wasn't "a tiny bit shameful that we can find nothing stronger than the word regret to describe the slaughter and misery and mayhem that Israel has unleashed on a fragile country like Lebanon".
The foreign secretary said that while she had "stringently condemned" Hezbollah, she had also tried to be "relatively proportionate" in what she said about all other players in the crisis.
"I can assure him that I am striving in every way that I can to act in a way that will be effective to bring about the situation that he desires," she said.
But the most effective action would not always be the same as what people wanted her to do.
And Hezbollah held the "simplest levers" to ending the conflict, by releasing captured Israeli soldiers, she said.
She told MPs Hezbollah had not had a "fig leaf" of justification for their initial attack on Israel.