The president's National Bipartisan Commission on Central America was sworn in yesterday, with all sides pledging a nonpartisan effort to agree on a long-term U.S. policy for the region.

The State Department's Latin American policy-making team also went to full strength with the unofficial designation of five deputies to Assistant Secretary Langhorne A. Motley. Motley's predecessor, Thomas O. Enders, never had more than two deputies in place during his two years in office.

At the swearing-in ceremony, commission Chairman Henry A. Kissinger pledged that the 12-member group would produce "the fullest and fairest report of which we are capable."

Joking that the presence of Texans on the commission "assures I won't be the only one speaking with an accent in our deliberations," Kissinger said that if the United States "can work out a cooperative pattern" with Central American nations, "it can be an example for our relations in the rest of the hemisphere and the rest of the world. And it will also help us define what we are resisting."

Secretary of State George P. Shultz, charging the group with finding ways "to make our neighborhood a healthier . . . and more secure one," noted that the effort will "take more than a fair share of your time." The commission began its first session immediately with a closed briefing from one of Motley's new deputies, L. Craig Johnstone, previously director of the department's office of Central American affairs.

The other new deputies expected to be named shortly, according to State Department officials, are Charles A. Gillespie, a former Enders assistant who will reportedly handle Caribbean affairs; Lowell C. Kilday, now director of Brazilian affairs, who will handle the Andean region; and Richard Holwill of the Heritage Foundation, for congressional and business affairs. Deputy Assistant Secretary James H. Michel becomes senior deputy.

Kissinger's commission is to meet today with President Reagan and to meet with Shultz over lunch Friday between briefings. The White House announced that two "senior counselors" will join U.N. Ambassador Jeane J. Kirkpatrick and eight members of Congress in advising the commission. The two senior counselors are William D. Rogers, former assistant secretary of state for Latin America under Kissinger, and Winston Lord, who was head of policy planning at Kissinger's State Department and now is president of the Council on Foreign Relations.

In a related event, an administration official said a meeting was expected "soon" between Salvadoran guerrilla leaders and an arm of the Salvadoran government, which other sources said would be the government's peace commission.

The official, who cannot be identified under the rules of the briefing, said "some positive steps" toward such talks were made in July when special Ambassador Richard B. Stone met with guerrilla spokesman Ruben Zamora. Stone's mission has been to bring the two sides together.

Besides Kissinger, the other 11 commission members:

* Nicholas F. Brady, 53, who served eight months as a New Jersey senator in 1982, and is chairman and a managing director of the New York investment banking firm of Dillon, Read & Co. A member of the Council on Foreign Relations, he is also a member of the President's Commission on Strategic Forces.

* Henry G. Cisneros, 36, mayor of San Antonio and professor in the social and policy sciences division of the University of Texas. Arriving at the ceremonies, he said U.S. policy in Central America had been seen as "too heavy-handed" because of "toppling governments and rigging elections." He said he hoped the administration's short-term actions would not preempt the commission's long-range efforts.

* Bill Clements, 66, former governor of Texas, who is also past president of the American Association of Oil Well Drilling Contractors. He was a deputy secretary of defense from 1973 to 1977.

* Carlos F. Diaz-Alejandro, 46, Yale University professor of economics, who was born in Cuba and became a U.S. citizen in 1974. A member of the Council on Foreign Relations and of several commissions on international economic affairs, he was criticized by Sen. Paula Hawkins (R-Fla.) and Cuban-American refugee groups as unacceptably close to Cuban President Fidel Castro. The White House has stood by his appointment.

* Wilson S. Johnson, president of the National Federation of Independent Business for 14 years. A Virginia native, he also serves on the president's Private Sector Survey on Cost Control.

* Lane Kirkland, 61, president of the AFL-CIO.

* Richard Scammon, social scientist and director of the Elections Research Center of Washington. Author of several works on American politics, he was one of 70 official U.S. observers of El Salvador's elections last year.

* John R. Silber, 56, president since 1971 of Boston University, one of the nation's largest private institutions, and a Texas native known for his outspokenness.

* Potter Stewart, 68, retired Supreme Court justice, a Republican who stepped down in 1981 after 23 years on the bench. He often cast the swing vote on controversial social issues and was known for his incisive writing style.

* Robert S. Strauss, 65, former chairman of the Democratic National Committee, a Texas lawyer and businessman. Arriving at the ceremonies yesterday, Strauss said he had "strong differences with the administration's Central American policy," but added that the commission "is not a political matter."

* Dr. William B. Walsh, 63, president of Project HOPE (Health Opportunity for People Everywhere), a medical education program based in Virginia. He is a heart specialist and professor of internal medicine at Georgetown University.