A group of approximately 500 of the nation's top business and financial leaders appears to have reached agreement on a national advertisement urging President Reagan and Congress to take dramatic steps to shrink the federal budget deficit, sources said yesterday. The advertisement is scheduled to appear in major newspapers next Thursday.

The advertisement, which will run under a heading describing it as a bipartisan appeal to resolve the budget crisis, will mark the start of a publicity campaign being run by six former government officials who believe the huge federal deficits now projected must be reduced. The group, headed by former Commerce secretary Peter G. Peterson, will outline the campaign at a Washington press conference next Wednesday, sources said.

The main recommendations of the group's campaign call for a reduction in the budget deficit for 1985 and later years. Specifically, the ad calls for:

$60 billion in cuts in domestic spending programs, principally concentrated on entitlement programs--such as Social Security--which benefit middle- and upper-income people as well as poor people, and which have not yet been cut back by much.

$25 billion in defense cuts.

$60 billion in unspecified tax increases, aimed at curbing consumption, rather than saving and investment.

These measures, if taken in 1985, would also cut $30 billion in interest payments on servicing the national debt, the advertisement says, and would reduce the deficit from $250 billion to $75 billion.

The measures would involve a substantial shift from Reagan's previous unwillingness to cut deeply into defense spending or increase taxes further. However, the signatories to the advertisement stress that it is not intended as a confrontation with the White House, sources involved in the appeal said yesterday. The call for new policies is aimed at Congress as well as at the president, the sources said.

The six founding members, who include five former Treasury secretaries as well as Peterson, will send a letter to the president, to Speaker of the House Thomas P. O'Neill (D-Mass.) and to Senate Majority Leader Howard Baker (R-Tenn.), along with a copy of the statement, the sources said. The letter will stress that today's fiscal crisis has its roots in the actions of all administrations of the past 20 years, including those in which they served, the sources said, and it will ask for a bipartisan, cooperative effort to curb deficits.

The advertisement also will stress the damage that has been done to the economy by the strength of the dollar. The dollar has been pushed up, in part by high interest rates, to a level where U.S. manufacturing industries have been badly hurt by competition from overseas. Deteriorating trade performance has accounted for a substantial part of the overall decline in the economy during the recession, the sources said.

The advertisement will also say that the conflict between tight monetary policy and loose fiscal policy has driven up interest rates and hurt the economy. And it will point out that some of the signatories believe that other measures are necessary, on top of the fiscal reform suggested, in order to get the economy moving. Some participants in the appeal, for example, favor an easing of monetary policy.