A group of 26 nations meeting under the chairmanship of the United States yesterday pledged to increase their financial support to the countries most severely affected by the Persian Gulf War and to step up the pace of their disbursements.

But Treasury Undersecretary David C. Mulford, announcing the results of the fourth meeting of the Gulf Crisis Coordinating Committee, reiterated U.S. concern about the slow pace of Japanese disbursements against its $2.1 billion pledge.

He also indicated that the European Community, as well as individual EC nations such as Germany, would be urged to increase the amounts they had promised to date.

Budget director Richard G. Darman yesterday reported that allied countries have promised the United States a total of $51.5 billion in cash and contributions of equipment and fuel. The pledges are "a very, very substantial portion of the actual costs incurred," he told reporters.

Of the pledges, more than $5.3 billion in cash has come to the Treasury and $1.3 billion in in-kind contributions has been received.

For accounting purposes, the cost of the U.S. military role in the gulf has been split into periods that follow the fiscal quarters. For the period from Aug. 2 through Dec. 31, 1990, the allies pledged $9.7 billion in cash and in-kind contributions: $3.3 billion from Saudi Arabia, $2.5 billion from Kuwait, $1.7 billion from Japan, $1.1 billion from Germany, $1 billion from the United Arab Emirates and a small amount from other nations. Of that, $5.3 billion in cash and 1.3 billion in in-kind contributions have been received.

The administration projects that the cost of the action though Dec. 31 was about $11.1 billion. If all the pledges are paid, that would leave the U.S. with about $1.4 billion to pay; Congress already has appropriated $2 billion to cover the gulf operation for this fiscal year.

For the period between Jan. 1 and March 31, 1991, Saudi Arabia has pledged $13.5 billion; Kuwait, $13.5 billion; Japan, $9 billion; Germany, $5.5 billion, and $280 million from Korea. All of the pledges after Dec. 31, 1990, are in cash. Some of the money has already been paid, although Darman would not give details.

"This isn't charity," Darman told the Senate Budget Committee. "This should be viewed as a thoroughly sound investment on their part."

Mulford, discussing the funds earmarked for aid to front-line states, listed disbursements yesterday at $6.7 billion, up from about $5 billion at the end of last November. The bulk of the money is destined for Egypt, Turkey and Jordan; most of the balance goes to smaller members of the coalition arrayed against Iraq.

Mulford would not divulge the separate totals for Egypt, Turkey and Jordan. Asked why Jordan should receive financial assistance, given that it is neither a member of the coalition fighting Iraq nor a supporter of the U.N. resolution demanding Iraq's withdrawal from Kuwait, Mulford said the coordinating group continues to consider Jordan a front-line state.

Mulford revealed that the bulk of Japan's aid to the front-line countries is in the form of concessional loans, rather than grants which constitute about two-thirds of the aid from other countries.

In expressing impatience with Japan, Mulford pointed out that Tokyo had disbursed only $400 million of its $2.1 billion pledge, or 19 percent, which he said compared unfavorably with a 59 percent disbursement ratio by the gulf oil states and 43 percent by the European community.

He said Japan had been asked for more grants and fewer loans.