WASHINGTON (AP) _ Taking aim at at suggestions in Congress for new taxes, President Reagan says such proposals ''have about as much chance of flying as a dead duck.''

Reagan, speaking to a group of conservative business supporters Friday, appeared to be responding to House Speaker Jim Wright of Texas, who has said the budget can't be balanced by spending cuts alone and has argued for the need to raise more revenue.

Saying ''there are some'' in Congress who want to back away from the Gramm- Rudman budget-balancing law's $108 billion deficit target for fiscal 1988, which starts Oct. 1, or have suggested that new taxes are needed, Reagan said they should know ''that's just not going to happen.''

''All these tax hike schemes have about as much chance of flying as a dead duck,'' Reagan said, adding: ''My pledge to veto any tax rate increase remains rock solid. There will be no tax rate increase in the (current) 100th Congress.''

House Budget Committee Chairman William H. Gray III issued an immediate and caustic response, challenging Reagan to submit an honestly balanced budget to Congress.

''The president should have learned from the Irangate affair to get full command of the facts before he speaks out,'' Gray said. ''His budget does not do what he claims... A president is supposed to lead. Let him lead.''

Gray's panel and its Senate counterpart will begin next week formally drafting their spending plans, and say they may fall as far short of the $108 billion deficit target for fiscal 1988 as Reagan did in his budget. By congressional estimates, the president's spending plan would leave a deficit of about $135 billion.