President Reagan said yesterday that he has "no illusions about Soviet intentions" at the forthcoming summit with Mikhail Gorbachev, but a senior administration official and a prominent Republican senator said the meeting could result in drafting "guidelines" for Geneva arms-control negotiators.

Reagan made the comment in a statement read to Republican congressional leaders at the White House, where he also said that "genuine improvement" in the U.S.-Soviet relationship would require progress on human-rights issues and on regional conflicts such as that in Afghanistan.

Administration sources said the president does not want to "raise expectations" that the Nov. 19-20 summit in Geneva is likely to produce a specific agreement.

But Senate Foreign Relations Committee Chairman Richard G. Lugar (R-Ind.) said it is "possible that there might be a statement of agreed ideas" at the summit coupled with "instructions or priorities" to U.S. arms-control negotiators. They are scheduled to resume talks in Geneva Jan. 16. Lugar attended the White House meeting and met this week with Secretary of State George P. Shultz.

Special arms-control adviser Paul H. Nitze, speaking to the Overseas Writers Club, said the two nations are considering "guidelines" for the arms negotiators "that would move the process forward."

Nitze said such guidelines would be helpful and added, "I think the executive branch agrees." But he said it is premature to say whether efforts to negotiate them with the Soviets will succeed.

Another official said the guidelines under discussion would be a very general statement of objectives for the arms negotiators, primarily drawn from past public pronouncements and positions of the two sides.

Nitze drew a sharp distinction between "guidelines" for negotiators and an "agreement in principle" of a less definite nature, such as the 1972 agreement on "Basic Principles of U.S.-Soviet Relations."

Such agreements have caused trouble because Washington and Moscow interpreted them differently, he said.

Soviet Foreign Minister Eduard Shevardnadze, in a speech to the United Nations Oct. 24, asked the United States to adopt positions that would make it possible for Reagan and Gorbachev "to reach an agreement on principle on the questions under discussion at the Geneva negotiations."

But Shultz, after meeting with Gorbachev and Shevardnadze in Moscow this week, said such an agreement appears unlikely.

Reporting to the GOP leaders, Shultz called his Moscow meetings "14 hours of painstaking, systematic" discussions of all summit issues.

He said the meetings, during which Gorbachev frequently interjected comments, were "not hostile, but vigorous."

In his remarks, Reagan said, "I am going to Geneva with a sense of confidence and knowledge based on the knowledge that over the past five years we have restored America's strength and understanding. I have no illusions about Soviet intentions and fundamental differences separating us."

Later, Reagan met with 19 religious leaders of various faiths to elicit summit views and ask them to pray for Gorbachev.

Ernest Gordon, president of a Christian group that tries to aid dissidents seeking to leave the Soviet, said, "One of the things that he asked all of us to do was pray for Gorbachev recognizing we're all God's children. In our prayers, we should remember that Gorbachev, indeed, is a creation of God."

Cardinal John J. O'Connor, Roman Catholic archbishop of New York, said Reagan was "responsive" to a plea from several members of the group to press for more liberal Soviet emigration policies and a halt to religious persecution.

Rabbi Stanley Rabinowitz of Adas Israel Synagogue, the largest Conservative Jewish temple in Washington, said the president behaved like a "statesman" at the meeting and clearly impressed the religious leaders.