The Agency for International Development asked Congress yesterday for permission to spend $3.4 million to help run the elections planned in El Salvador late this year. The government of El Salvador is planning to spend another $4.9 million.

The elections, State Department officials said, "will have to be purer than pure for the sake of credibility." That is the purpose of the funds, which AID said would support only measures that do not favor one party or another.

But the request could come under fire in Congress as another step toward increased American involvement in the affairs of El Salvador, where President Reagan also is pushing for higher military aid.

Chairmen of four congressional committees--House Foreign Affairs, Senate Foreign Relations and both House and Senate Appropriations committees--have 15 days to veto the election proposal, and some resistance is expected.

The $3.4 million figure "will raise some eyebrows," one House aide observed.

Sen. Nancy Landon Kassebaum (R-Kan.) said in a speech last month that the project "will only confirm to some critics that this election is made in the U.S.A., and that we are trying, in effect, to buy it."

However, Congress has been insistent on the value of free elections in El Salvador and has a crowded agenda for the next three weeks that would make it difficult to schedule hearings within the allotted time. AID officials also took careful soundings beforehand, discussing the funding proposal with congressional leaders and assuring them that El Salvador's government will carry the brunt of the costs.

AID spent $440,000 to support the March, 1982, general assembly elections in El Salvador, half on the expenses of 70 observers and the rest on a get-out-the vote media campaign.

Leftist groups, which boycotted the polling, charged that the 1.3 million ballots cast could not have been possible except by fraud, but no method for the fraud was ever spelled out.

At the same time, the left's refusal to participate in the elections, and subsequent criticism of the outcome, stemmed not from serious charges that they were fraudulent, but from a belief that, without the security that would allow the left to participate, they were relatively meaningless.

Under the AID request, the money would be reallocated from so-called economic support funds already appropriated. The U.S. contribution would provide a computer to upgrade voting lists and count ballots, 69 "worker-months" of help from U.S. technical advisers and teachers and transport, food and lodging for 200 international observers to make two trips there and back.

The Salvadorans would pay to train people to run the computer, and in addition would finance a media campaign to get people to the polls, ballot printing, salaries and security for the election, tentatively set for November, and for the presidential runoff in December.

The proposal is divided in four parts.

* A Wang VS computer system, chosen because it can be delivered as early as the first of next month, will be sent to El Salvador along with a four-member team of experts on voter registration and data management to "clean up the voter registry list," a State Department official said.

When the new list is published and publicized, voters not on the list will have about two months to persuade officials they should be included in a revised list.

The $1.15 million computer system includes a maintenance contract, power source, microfilm equipment and a service contract. A professional U.S. auditing firm will be contracted at $400,000 to monitor and verify the vote count.

* The Salvadoran government will spend $600,000 to contract with a media consulting firm of unspecified nationality that will publicize the elections so as to induce people to go to the polls.

* About 200 international observers will be brought to El Salvador and taken to voting sites around the country at a cost of $780,000.

* AID will send a team of four trainers to aid the Salvadorans in running the elections, at a cost of $220,000.

El Salvador will spend $2.9 million to run them, not counting military security costs.