"Please hurry," he told NATO leaders at a public session of the Euro-Atlantic Partnership Council, which groups 26 members of the alliance and 20 other countries.
"The Afghan people need that security today, not tomorrow," Karzai said.
NATO leaders agreed at the start of a two-day summit on Monday to make available an additional 3,500 troops for the presidential and legislative elections in Afghanistan.
"Our request today is to please fulfil the commitment you have made ... so that we can provide our people with an environment in which they can go and vote freely and fairly," Karzai said.
He put a brave face on the limited expansion of NATO's peace force in his violence-plagued country despite UN warnings that a lack of foreign troops could derail elections in September.
Before Karzai arrived, his spokesman had complained that NATO planned to deploy forces only to Kabul and the relatively stable north of the country.
"We need NATO to expand to all areas where security is not good, not just to the north," Hamid Elmi said.
Karzai, standing alongside NATO Secretary-General Jaap de Hoop Scheffer, told a news conference he was not disappointed.
"The idea was not that NATO would be deployed all over the country for security for elections," he said. "The idea was that they would be deployed in the part of the country that has been decided yesterday, and we are happy with that."
"The Afghan people need that security today, not tomorrow"
Interim Afghan President
But there was less diplomatic nicety in Kabul, where Defence Ministry spokesman General Zahir Azimy told Reuters: "It's up to ... NATO, but this is not sufficient, we expect more".
Karzai insisted that the elections must be held in September, and said that with some 5.2 million of an estimated electorate of 9.5-9.8 million already registered to vote this was "very much possible".
United Nations Secretary-General Kofi Annan, complaining that there were not enough NATO troops on the ground, said last week that the landmark vote could only go ahead on schedule if the security situation was tamed.
NATO has agreed to widen the influence of its International Security Assistance Force by taking over four special "reconstruction teams" in the north, which try to underpin aid and development projects by keeping a lid on violence.
The election has been repeatedly
postposed for security reasons
They also agreed to reinforce Provincial Reconstruction Teams (PRTs) and deploy a quick-reaction force of 600 troops to Kabul to bolster security during the landmark vote.
NATO hoped to announce that PRTs were set up in the west, but this was thwarted by member reluctance to offer costly kit such as transport planes, helicopters and medical facilities.
However, it argues that security in the south and east is provided by a 20,000-strong US-led combat force pursuing the Taliban and their al Qaeda network allies.
This force has stepped up operations to protect the polls, which many analysts say US President George Bush wants to see held on time in the hope of a policy success to balance against Iraq in the run-up to his November re-election bid.
Bush was due to give a speech on Tuesday at a university in Istanbul hailing Monday's transfer of power in Baghdad as an opportunity for both Iraq and the wider Middle East region.
But his efforts to portray the alliance as united once more after the divisions sparked by last year's Iraq war were undermined by French President Jacques Chirac's remarks that he still opposed a formal NATO presence in the country.
The alliance also agreed to train Iraqi security forces after Monday's formal handover to an interim government in Baghdad, though France marred a mood of renewed transatlantic amity.
George Bush was criticised for his support of Turkey's bid to join the European Union and was told that it was none of his business
The training deal is also much more modest than the troop deployment Washington had initially sought from the alliance that was scotched by French and German resistance.
Chirac, a leading opponent of the Iraq war, further soured the summit mood by criticising Bush's support for Turkey's bid to join the European Union, saying it was none of his business.
He also vetoed a US proposal to send elements of the elite NATO Response Force to Afghanistan during the elections.