A Reagan administration proposal to increase foreign aid by 23 percent next year ran into heavy weather yesterday from the budget-conscious Senate Foreign Relations Committee.

"We are going to have some serious objections," Chairman Charles H. Percy (R-Ill.) warned Undersecretary of State James L. Buckley on the opening day of hearings on an $8.7 billion military and economic assistance package for fiscal 1983.

"Foreign assistance doesn't fly very well in Peoria nor in most other parts of the country," Percy added.

"A very heavy burden of proof rests on the administration to justify the increase at a time of budget austerity," said Sen. Claiborne Pell (D-R.I.), the panel's ranking minority member.

The proposed increases fall almost entirely in the area of arms credits and loan guarantees, with the administration seeking to lift its foreign military sales program by $1.6 billion over the $4.1 billion already authorized by Congress for fiscal 1983.

Israel and Egypt would be the largest beneficiaries of the increases, with $2.5 billion in combined aid going to Israel, including a $500 million forgiveness on past loans to purchase military equipment. Egypt would get $2 billion, including a $400 million loan waiver. This fiscal year Israel received $2.2 billion and Egypt $1.7 billion.

Other countries that would receive substantial military aid increases under the administration plan include Spain (up from $125 million in fiscal 1982 to $400 million), with which the United States is negotiating a treaty to permit continued use of air and naval bases; Turkey (up from $703 million to $819 million), which the United States is trying to help fulfill its NATO commitments, and Pakistan (up from $100 million to $451 million), which the United States seeks to bolster because it borders Soviet-occupied Afghanistan.

The budget also proposes small military aid authorizations for Argentina, Chile and Guatemala, which were cut off by the Carter administration in 1977 for human rights violations.

Percy yesterday asked Buckley whether, in light of the Argentine takeover of the Falkland Islands and Justice Department concerns over the 1976 assassination here of former Chilean diplomat Orlando Letelier, the administration would go ahead with $50,000 in military training funds for each of those countries.

"Both matters are under very careful review," Buckley said.

He was similarly noncommittal when asked if the administration would decline to certify funds to El Salvador in the event that a right-wing coalition peels back the land reforms of the regime of Jose Napoleon Duarte.

"I don't think it would be helpful at this stage to second-guess political developments in El Salvador," he said. The administration budget calls for $166 million in aid, roughly two-thirds of it economic and one-third military, to that war-torn country.

While there were scattered questions about the details of the aid program, most of the senators' attention was focused on how the administration could call for increases in the defense budget and foreign military aid simultaneously while trying to trim all other parts of the budget.

"It is becoming increasingly difficult to vote for foreign aid programs when we are having budgetary difficulties here at home," said Sen. Larry Pressler (R-S.D.).

"It's a little tough for me to look at foreign aid increases when we have farmers going down the tube in this country because they can't get any money," said Sen. Jesse Helms (R-N.C.).

Buckley listened impassively, then said of the proposed increases, "When an arsonist is on the loose, you don't get rid of the fire department."

He said there is a need to keep allies well-armed, and called such military assistance "the most cost-effective investment we can make."